Add clang-format configuration.

.clang-format

@@ -0,0 +1,28 @@
+
+BasedOnStyle: LLVM
+IndentWidth: 2
+ColumnLimit: 80
+
+Language: Cpp
+Standard: Cpp11
+DerivePointerAlignment: false
+PointerAlignment: Left
+
+AlignAfterOpenBracket: Align
+PenaltyBreakBeforeFirstCallParameter: 50
+AlignOperands: true
+AllowShortIfStatementsOnASingleLine: true
+AllowShortCaseLabelsOnASingleLine: true
+IndentCaseLabels: true
+
+IncludeCategories:
+  - Regex:           '^"[^/]+\"'
+    Priority:        10
+  - Regex:           '^"cling/'
+    Priority:        20
+  - Regex:           '^"clang/'
+    Priority:        30
+  - Regex:           '^"llvm/'
+    Priority:        40
+  - Regex:           '^<'
+    Priority:        50