re-add a trimmed version of clang-format.

.clang-format

@@ -0,0 +1,98 @@
+---
+BasedOnStyle: GNU
+Language:        Cpp
+AlignAfterOpenBracket: DontAlign
+AlignArrayOfStructures: Left
+AlignConsecutiveAssignments:
+  Enabled:         true
+  AlignFunctionDeclarations: true
+AlignConsecutiveBitFields:
+  Enabled:         true
+  AcrossEmptyLines: true
+  AlignFunctionDeclarations: true
+AlignConsecutiveDeclarations:
+  Enabled:         true
+  PadOperators:    true
+AlignConsecutiveMacros:
+  Enabled:         true
+  AcrossEmptyLines: true
+  AlignFunctionDeclarations: true
+  PadOperators:    true
+AlignConsecutiveShortCaseStatements:
+  Enabled:         true
+AlignEscapedNewlines: Left
+AlignOperands:   DontAlign
+AllowShortBlocksOnASingleLine: Always
+AllowShortCaseLabelsOnASingleLine: true
+AllowShortCompoundRequirementOnASingleLine: true
+AllowShortLoopsOnASingleLine: true
+BraceWrapping:
+  AfterCaseLabel:  false
+  AfterClass:      false
+  AfterControlStatement: Never
+  AfterEnum:       false
+  AfterExternBlock: false
+  AfterFunction:   true
+  AfterNamespace:  false
+  AfterObjCDeclaration: false
+  AfterStruct:     false
+  AfterUnion:      false
+  BeforeCatch:     false
+  BeforeElse:      false
+  BeforeLambdaBody: false
+  BeforeWhile:     false
+  IndentBraces:    false
+BreakAfterReturnType: Automatic
+BreakBeforeBinaryOperators: None
+BreakBeforeConceptDeclarations: Never
+BreakBeforeBraces: Custom
+BreakBeforeTernaryOperators: false
+BreakStringLiterals: false
+BreakTemplateDeclarations: MultiLine
+ColumnLimit:     0
+ConstructorInitializerIndentWidth: 8
+ContinuationIndentWidth: 8
+Cpp11BracedListStyle: true
+IncludeBlocks:   Regroup
+IncludeCategories:
+  - Regex:           '^<.*>'
+    Priority:        2
+    SortPriority:    0
+    CaseSensitive:   true
+  - Regex:           '^".*"'
+    Priority:        3
+    SortPriority:    0
+    CaseSensitive:   true
+  - Regex:           '.*'
+    Priority:        1
+    SortPriority:    0
+    CaseSensitive:   false
+IncludeIsMainRegex: '([-_](test|unittest))?$'
+IndentGotoLabels: false
+IndentRequiresClause: false
+IndentWidth:     8
+LineEnding:      LF
+MaxEmptyLinesToKeep: 2
+PackConstructorInitializers: NextLine
+PenaltyBreakAssignment: 10
+PenaltyBreakBeforeFirstCallParameter: 19
+PenaltyBreakBeforeMemberAccess: 150
+PenaltyBreakComment: 300
+PenaltyBreakFirstLessLess: 120
+PenaltyBreakOpenParenthesis: 0
+PenaltyBreakScopeResolution: 500
+PenaltyBreakString: 1000
+PenaltyBreakTemplateDeclaration: 10
+PenaltyExcessCharacter: 1000000
+PenaltyIndentedWhitespace: 0
+PenaltyReturnTypeOnItsOwnLine: 60
+QualifierAlignment: Left
+SpaceBeforeParens: ControlStatements
+SpaceBeforeParensOptions:
+  AfterControlStatements: true
+  AfterForeachMacros: true
+  AfterIfMacros:   true
+SpaceInEmptyBlock: true
+SpacesInContainerLiterals: false
+Standard:        Auto
+UseTab:          ForContinuationAndIndentation