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/itkNormalizedCorrelationTwoImageToOneImageMetric.h

@@ -40,16 +40,15 @@ namespace itk
  * \ingroup RegistrationMetrics
  * \ingroup TwoProjectionRegistration
  */
-template < typename TFixedImage, typename TMovingImage >
-class NormalizedCorrelationTwoImageToOneImageMetric :
-    public TwoImageToOneImageMetric< TFixedImage, TMovingImage >
+template <typename TFixedImage, typename TMovingImage>
+class NormalizedCorrelationTwoImageToOneImageMetric : public TwoImageToOneImageMetric<TFixedImage, TMovingImage>
 {
 public:
   ITK_DISALLOW_COPY_AND_ASSIGN(NormalizedCorrelationTwoImageToOneImageMetric);
 
   /** Standard class type alias. */
   using Self = NormalizedCorrelationTwoImageToOneImageMetric;
-  using Superclass = TwoImageToOneImageMetric<TFixedImage, TMovingImage >;
+  using Superclass = TwoImageToOneImageMetric<TFixedImage, TMovingImage>;
 
   using Pointer = SmartPointer<Self>;
   using ConstPointer = SmartPointer<const Self>;
@@ -78,37 +77,41 @@ class NormalizedCorrelationTwoImageToOneImageMetric :
 
 
   /** Get the derivatives of the match measure. */
-  void GetDerivative( const TransformParametersType & parameters,
-                      DerivativeType & Derivative ) const override;
+  void
+  GetDerivative(const TransformParametersType & parameters, DerivativeType & Derivative) const override;
 
   /**  Get the value for single valued optimizers. */
-  MeasureType GetValue( const TransformParametersType & parameters ) const override;
+  MeasureType
+  GetValue(const TransformParametersType & parameters) const override;
 
   /**  Get value and derivatives for multiple valued optimizers. */
-  void GetValueAndDerivative( const TransformParametersType & parameters,
-                              MeasureType& Value, DerivativeType& Derivative ) const override;
+  void
+  GetValueAndDerivative(const TransformParametersType & parameters,
+                        MeasureType &                   Value,
+                        DerivativeType &                Derivative) const override;
 
   /** Set/Get SubtractMean boolean. If true, the sample mean is subtracted
    * from the sample values in the cross-correlation formula and
    * typically results in narrower valleys in the cost fucntion.
    * Default value is false. */
-  itkSetMacro( SubtractMean, bool );
-  itkGetConstReferenceMacro( SubtractMean, bool );
-  itkBooleanMacro( SubtractMean );
+  itkSetMacro(SubtractMean, bool);
+  itkGetConstReferenceMacro(SubtractMean, bool);
+  itkBooleanMacro(SubtractMean);
 
 protected:
   NormalizedCorrelationTwoImageToOneImageMetric();
-  ~NormalizedCorrelationTwoImageToOneImageMetric() override {};
-  void PrintSelf(std::ostream& os, Indent indent) const override;
+  ~NormalizedCorrelationTwoImageToOneImageMetric() override{};
+  void
+  PrintSelf(std::ostream & os, Indent indent) const override;
 
 private:
-  bool    m_SubtractMean;
+  bool m_SubtractMean;
 };
 
 } // end namespace itk
 
 #ifndef ITK_MANUAL_INSTANTIATION
-#include "itkNormalizedCorrelationTwoImageToOneImageMetric.hxx"
+#  include "itkNormalizedCorrelationTwoImageToOneImageMetric.hxx"
 #endif
 
 #endif