Add clang-format file, based on that from Minetest

.clang-format

@@ -0,0 +1,45 @@
+BasedOnStyle: LLVM
+IndentWidth: 4
+UseTab: Always
+TabWidth: 4
+BreakBeforeBraces: Custom
+Standard: c++17
+BraceWrapping:
+  AfterClass: true
+  AfterControlStatement: Never
+  AfterEnum: true
+  AfterFunction: true
+  AfterNamespace: true
+  AfterStruct: true
+  AfterUnion: true
+  BeforeCatch: false
+  BeforeElse: false
+FixNamespaceComments: false
+AllowShortIfStatementsOnASingleLine: false
+IndentCaseLabels: false
+AccessModifierOffset: -4
+ColumnLimit: 0
+AllowShortFunctionsOnASingleLine: InlineOnly
+SortIncludes: Never
+IncludeCategories:
+  - Regex:           '^".*'
+    Priority:        2
+  - Regex:           '^<.*'
+    Priority:        1
+AlignAfterOpenBracket: DontAlign
+ContinuationIndentWidth: 8
+ConstructorInitializerIndentWidth: 8
+BreakConstructorInitializers: AfterColon
+AlwaysBreakTemplateDeclarations: Yes
+NamespaceIndentation: None
+PointerAlignment: Right
+SpaceAfterTemplateKeyword: true
+SpaceBeforeAssignmentOperators: true
+SpaceBeforeParens: ControlStatements
+SpaceInEmptyParentheses: false
+SpacesBeforeTrailingComments: 1
+SpacesInAngles: false
+SpacesInContainerLiterals: false
+SpacesInCStyleCastParentheses: false
+SpacesInParentheses: false
+SpacesInSquareBrackets: false