Add formatting tools

.clang-format

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+---
+BasedOnStyle: LLVM
+AllowShortBlocksOnASingleLine: 'true'
+AllowShortCaseLabelsOnASingleLine: 'true'
+AllowShortFunctionsOnASingleLine: Inline
+AllowShortIfStatementsOnASingleLine: WithoutElse
+AllowShortLambdasOnASingleLine: Inline
+AllowShortLoopsOnASingleLine: 'false'
+AlwaysBreakBeforeMultilineStrings: 'true'
+IndentWidth: '4'
+
+...

tools/format.sh

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+#!/bin/bash
+
+if [[ "$OSTYPE" == "darwin"* ]]; then
+  clang_format_command="clang-format"
+  clang_tidy_command="run-clang-tidy"
+fi
+if [[ "$OSTYPE" == "linux"* ]]; then
+  clang_format_command="clang-format-11"
+  clang_tidy_command="run-clang-tidy-11"
+fi
+
+eval "$clang_format_command -i *.h *.cpp -style=file"
+eval "$clang_tidy_command -fix"