Keep multiline array literals at same indent.

If the current line and the line above both begin with an array literal, align
the current line with the above line.
Resolves JesseKPhillips#26.

Keeps multiline 2D array definitions aligned like so:
auto a = [
  [1, 2, 3],
  [1, 2, 3],
  [1, 2, 3],
];

Previously they were aligned like so:
auto a = [
  [1, 2, 3],
  [1, 2, 3],
    [1, 2, 3],
];

indent/d.vim

@@ -65,5 +65,13 @@ function GetDIndent()
     return cindent(lnum - 1)
   endif
 
+  " Align multiline array literals. e.g.:
+  " auto a = [
+  "   [ 1, 2, 3 ],
+  "   [ 4, 5, 6 ],
+  if line =~ '^\s*\[' && getline(lnum - 1) =~ '^\s*\['
+    return indent(lnum - 1)
+  endif
+
   return cind
 endfunction

tests/array.d

@@ -0,0 +1,10 @@
+// Nothing should change when you reindent (press =G from the top)
+
+unittest {
+  auto a = [
+    [ 1, 2, 3, 4 ],
+    [ 1, 2, 3, 4 ],
+    [ 1, 2, 3, 4 ],
+    [ 1, 2, 3, 4 ],
+  ];
+}