Add .clang-format and apply it

.clang-format

@@ -0,0 +1,54 @@
+---
+AlwaysBreakTemplateDeclarations: true
+BreakBeforeBraces: Custom
+BraceWrapping:
+  AfterClass: true
+  AfterFunction: true
+  AfterStruct: true
+  AfterUnion: true
+  IndentBraces: false
+  BeforeElse: true
+  BeforeCatch: true
+BreakStringLiterals: true
+ColumnLimit: 100
+CompactNamespaces: true
+ContinuationIndentWidth: 2
+Cpp11BracedListStyle: true
+FixNamespaceComments: true
+IncludeBlocks: Regroup
+IncludeCategories:
+  - Regex:           '^".*-messages\.hh"$'
+    Priority:        3
+  - Regex:           '<catch2/'
+    Priority:        20
+  - Regex:           '^"util/'
+    Priority:        2
+  - Regex:           '^"gd/(libgen|nl_types)\.h"$'
+    Priority:        0
+  - Regex:           '^"gd/'
+    Priority:        1
+  - Regex:           '<[[:alnum:]_.]+>'
+    Priority:        100
+IndentPPDirectives: AfterHash
+IndentWidth: 2
+IndentWrappedFunctionNames: false
+KeepEmptyLinesAtTheStartOfBlocks: false
+Language: Cpp
+MaxEmptyLinesToKeep: 1
+NamespaceIndentation: None
+PointerAlignment: Left
+ReflowComments: true
+SortIncludes: true
+SortUsingDeclarations: true
+SpaceAfterCStyleCast: false
+SpaceAfterLogicalNot: false
+SpaceAfterTemplateKeyword: false
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeCpp11BracedList: false
+SpaceBeforeCtorInitializerColon: true
+SpaceBeforeInheritanceColon: true
+SpaceBeforeParens: ControlStatements
+SpacesBeforeTrailingComments: 2
+SpacesInAngles: false
+Standard: Cpp11
+...