source: add a clang-format file

.clang-format

+BasedOnStyle: Mozilla
+BreakBeforeBraces: Mozilla
+AccessModifierOffset: -4
+ColumnLimit: 79
+UseTab: Never
+IndentWidth: 4
+BinPackArguments: false
+BinPackParameters: false
+Standard: Cpp11
+AlignOperands: true
+AlignTrailingComments: true
+AllowShortBlocksOnASingleLine: false
+AllowShortCaseLabelsOnASingleLine: false
+AllowShortFunctionsOnASingleLine: None
+IndentCaseLabels: false
+MaxEmptyLinesToKeep: 1
+NamespaceIndentation: None