ENH: Add .gitattributes to allow running ITK clang-formatting scripts

```
git filter-branch -f \
--tree-filter "~/ITK/Utilities/Maintenance/clang-format.bash --clang-format ~/Dashboard/src/ITK-clang11/clang-format-Linux --tracked" \
    master..
```

.clang-format

@@ -0,0 +1,151 @@
+## This config file is only relevant for clang-format version 8.0.0
+##
+## Examples of each format style can be found on the in the clang-format documentation
+## See: https://clang.llvm.org/docs/ClangFormatStyleOptions.html for details of each option
+##
+## The clang-format binaries can be downloaded as part of the clang binary distributions
+## from http://releases.llvm.org/download.html
+##
+## Use the script Utilities/Maintenance/clang-format.bash to faciliate
+## maintaining a consistent code style.
+##
+## EXAMPLE apply code style enforcement before commit:
+#     Utilities/Maintenance/clang-format.bash --clang ${PATH_TO_CLANG_FORMAT_8.0.0} --modified
+## EXAMPLE apply code style enforcement after commit:
+#     Utilities/Maintenance/clang-format.bash --clang ${PATH_TO_CLANG_FORMAT_8.0.0} --last
+---
+# This configuration requires clang-format version 8.0.0 exactly.
+BasedOnStyle: Mozilla
+Language:        Cpp
+AccessModifierOffset: -2
+AlignAfterOpenBracket: Align
+AlignConsecutiveAssignments: false
+AlignConsecutiveDeclarations: true
+AlignEscapedNewlines: Right
+AlignOperands:   true
+AlignTrailingComments: true
+# clang 9.0 AllowAllArgumentsOnNextLine: true
+# clang 9.0 AllowAllConstructorInitializersOnNextLine: true
+AllowAllParametersOfDeclarationOnNextLine: false
+AllowShortBlocksOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: Inline
+# clang 9.0 AllowShortLambdasOnASingleLine: All
+# clang 9.0 features AllowShortIfStatementsOnASingleLine: Never
+AllowShortIfStatementsOnASingleLine: false
+AllowShortLoopsOnASingleLine: false
+AlwaysBreakAfterDefinitionReturnType: None
+AlwaysBreakAfterReturnType: All
+AlwaysBreakBeforeMultilineStrings: false
+AlwaysBreakTemplateDeclarations: Yes
+BinPackArguments: false
+BinPackParameters: false
+BreakBeforeBraces: Custom
+BraceWrapping:
+  # clang 9.0 feature AfterCaseLabel:  false
+  AfterClass:      true
+  AfterControlStatement: true
+  AfterEnum:       true
+  AfterFunction:   true
+  AfterNamespace:  true
+  AfterObjCDeclaration: true
+  AfterStruct:     true
+  AfterUnion:      true
+  AfterExternBlock: true
+  BeforeCatch:     true
+  BeforeElse:      true
+## This is the big change from historical ITK formatting!
+# Historically ITK used a style similar to https://en.wikipedia.org/wiki/Indentation_style#Whitesmiths_style
+# with indented braces, and not indented code.  This style is very difficult to automatically
+# maintain with code beautification tools.  Not indenting braces is more common among
+# formatting tools.
+  IndentBraces:    false
+  SplitEmptyFunction: false
+  SplitEmptyRecord: false
+  SplitEmptyNamespace: false
+BreakBeforeBinaryOperators: None
+#clang 6.0 BreakBeforeInheritanceComma: true
+BreakInheritanceList: BeforeComma
+BreakBeforeTernaryOperators: true
+#clang 6.0 BreakConstructorInitializersBeforeComma: true
+BreakConstructorInitializers: BeforeComma
+BreakAfterJavaFieldAnnotations: false
+BreakStringLiterals: true
+## The following line allows larger lines in non-documentation code
+ColumnLimit:     120
+CommentPragmas:  '^ IWYU pragma:'
+CompactNamespaces: false
+ConstructorInitializerAllOnOneLineOrOnePerLine: false
+ConstructorInitializerIndentWidth: 2
+ContinuationIndentWidth: 2
+Cpp11BracedListStyle: false
+DerivePointerAlignment: false
+DisableFormat:   false
+ExperimentalAutoDetectBinPacking: false
+FixNamespaceComments: true
+ForEachMacros:
+  - foreach
+  - Q_FOREACH
+  - BOOST_FOREACH
+IncludeBlocks:   Preserve
+IncludeCategories:
+  - Regex:           '^"(llvm|llvm-c|clang|clang-c)/'
+    Priority:        2
+  - Regex:           '^(<|"(gtest|gmock|isl|json)/)'
+    Priority:        3
+  - Regex:           '.*'
+    Priority:        1
+IncludeIsMainRegex: '(Test)?$'
+IndentCaseLabels: true
+IndentPPDirectives: AfterHash
+IndentWidth:     2
+IndentWrappedFunctionNames: false
+JavaScriptQuotes: Leave
+JavaScriptWrapImports: true
+KeepEmptyLinesAtTheStartOfBlocks: true
+MacroBlockBegin: ''
+MacroBlockEnd:   ''
+MaxEmptyLinesToKeep: 2
+NamespaceIndentation: None
+ObjCBinPackProtocolList: Auto
+ObjCBlockIndentWidth: 2
+ObjCSpaceAfterProperty: true
+ObjCSpaceBeforeProtocolList: false
+PenaltyBreakAssignment: 2
+PenaltyBreakBeforeFirstCallParameter: 19
+PenaltyBreakComment: 300
+## The following line allows larger lines in non-documentation code
+PenaltyBreakFirstLessLess: 120
+PenaltyBreakString: 1000
+PenaltyBreakTemplateDeclaration: 10
+PenaltyExcessCharacter: 1000000
+PenaltyReturnTypeOnItsOwnLine: 200
+PointerAlignment: Middle
+ReflowComments:  true
+# We may want to sort the includes as a separate pass
+SortIncludes:    false
+# We may want to revisit this later
+SortUsingDeclarations: false
+SpaceAfterCStyleCast: false
+# SpaceAfterLogicalNot: false
+SpaceAfterTemplateKeyword: true
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeCpp11BracedList: false
+SpaceBeforeCtorInitializerColon: true
+SpaceBeforeInheritanceColon: true
+SpaceBeforeParens: ControlStatements
+SpaceBeforeRangeBasedForLoopColon: true
+SpaceInEmptyParentheses: false
+SpacesBeforeTrailingComments: 1
+SpacesInAngles:  false
+SpacesInContainerLiterals: false
+SpacesInCStyleCastParentheses: false
+SpacesInParentheses: false
+SpacesInSquareBrackets: false
+Standard:        Cpp11
+StatementMacros:
+  - Q_UNUSED
+  - QT_REQUIRE_VERSION
+TabWidth:        2
+UseTab:          Never
+...

.gitattributes

@@ -0,0 +1,14 @@
+# Custom attribute to mark sources as using our C++/C code style.
+[attr]our-c-style  whitespace=tab-in-indent,no-lf-at-eof  hooks.style=KWStyle,clangformat
+
+*.c              our-c-style
+*.h              our-c-style
+*.cxx            our-c-style
+*.hxx            our-c-style
+*.txx            our-c-style
+*.txt            whitespace=tab-in-indent,no-lf-at-eof
+*.cmake          whitespace=tab-in-indent,no-lf-at-eof
+
+# ExternalData content links must have LF newlines
+*.md5            crlf=input
+*.sha512         crlf=input

include/itkMultipleImageIterator.h

@@ -1,78 +1,94 @@
 /*=========================================================================
-*
-*  Copyright Insight Software Consortium
-*
-*  Licensed under the Apache License, Version 2.0 (the "License");
-*  you may not use this file except in compliance with the License.
-*  You may obtain a copy of the License at
-*
-*         http://www.apache.org/licenses/LICENSE-2.0.txt
-*
-*  Unless required by applicable law or agreed to in writing, software
-*  distributed under the License is distributed on an "AS IS" BASIS,
-*  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-*  See the License for the specific language governing permissions and
-*  limitations under the License.
-*
-*=========================================================================*/
+ *
+ *  Copyright Insight Software Consortium
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
 
 #ifndef itkMultipleImageIterator_h
 #define itkMultipleImageIterator_h
 #include <vector>
 #include <itkImageRegionIterator.h>
 
 
-namespace itk {
-  /** \class MultipleImageIterator
-   * \brief An wrapper around image iterators to iterate over several images simultaneously 
-   * All iterators must
-   *  - point to images of the same type
-   *  - be of the same size (number of values from begin to end)
-   * \ingroup MultipleImageIterator */
-template<typename TIterator>
-class MultipleImageIterator {
+namespace itk
+{
+/** \class MultipleImageIterator
+ * \brief An wrapper around image iterators to iterate over several images simultaneously
+ * All iterators must
+ *  - point to images of the same type
+ *  - be of the same size (number of values from begin to end)
+ * \ingroup MultipleImageIterator */
+template <typename TIterator>
+class MultipleImageIterator
+{
 public:
   using Self = MultipleImageIterator;
   using IteratorType = TIterator;
   using ImageType = typename IteratorType::ImageType;
   /// Access one of the iterators
-  IteratorType& operator[](const int i) {return m_Iterators[i];}
+  IteratorType & operator[](const int i) { return m_Iterators[i]; }
   /// Add a new iterator
-  void AddIterator(const IteratorType& it) {m_Iterators.push_back(it);}
+  void
+  AddIterator(const IteratorType & it)
+  {
+    m_Iterators.push_back(it);
+  }
   /// Advance all iterators
-  Self& operator++() {
-    for (auto it = m_Iterators.begin();
-      it != m_Iterators.end(); ++it) {
+  Self &
+  operator++()
+  {
+    for (auto it = m_Iterators.begin(); it != m_Iterators.end(); ++it)
+    {
       ++(*it);
     }
     return *this;
   }
   /// Rewind all iterators
-  void GoToBegin() {
-    for (auto it = m_Iterators.begin();
-      it != m_Iterators.end(); ++it) {
+  void
+  GoToBegin()
+  {
+    for (auto it = m_Iterators.begin(); it != m_Iterators.end(); ++it)
+    {
       it->GoToBegin();
     }
   }
   /** Check if the first iterator is at end. In debug mode, additionally check
-   * that at least one iterator is present and that all iterators' IsAtEnd() 
+   * that at least one iterator is present and that all iterators' IsAtEnd()
    * methods return the same thing */
-  bool IsAtEnd() {
+  bool
+  IsAtEnd()
+  {
 #ifdef NDEBUG
     return m_Iterators[0].IsAtEnd();
 #else
     assert(m_Iterators.size());
     bool retval = m_Iterators[0].IsAtEnd();
-    for (unsigned int i=0; i<m_Iterators.size();++i)
+    for (unsigned int i = 0; i < m_Iterators.size(); ++i)
       assert(m_Iterators[i].IsAtEnd() == retval);
     return retval;
 #endif
   }
   /// Returns the number of iterators
-  unsigned int Size () const { return m_Iterators.size(); }
+  unsigned int
+  Size() const
+  {
+    return m_Iterators.size();
+  }
+
 protected:
   std::vector<IteratorType> m_Iterators;
-
 };
-}
-#endif //itkMultipleImageIterator_h
+} // namespace itk
+#endif // itkMultipleImageIterator_h