Add clang script and .clang example (#52)

Basic usage:
clang-format-all src/

Advanced usage:
clang-format-all project1/ project2/ project3/

.clang-format-2

@@ -0,0 +1,13 @@
+# clang-format
+---
+Language: Cpp
+BasedOnStyle: LLVM
+AccessModifierOffset: -4
+IndentWidth: 4
+
+# Our includes are not order-agnostic
+SortIncludes: false
+
+# Some of our comments include insightful insight
+ReflowComments: false
+...

clang-format-all

@@ -0,0 +1,84 @@
+#!/bin/bash
+#
+# clang-format-all: a tool to run clang-format on an entire project
+# Copyright (C) 2016 Evan Klitzke <evan@eklitzke.org>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+function usage {
+    echo "Usage: $0 DIR..."
+    exit 1
+}
+
+if [ $# -eq 0 ]; then
+    usage
+fi
+
+# Variable that will hold the name of the clang-format command
+FMT=""
+
+# Some distros just call it clang-format. Others (e.g. Ubuntu) are insistent
+# that the version number be part of the command. We prefer clang-format if
+# that's present, otherwise we work backwards from highest version to lowest
+# version.
+for clangfmt in clang-format{,-{4,3}.{9,8,7,6,5,4,3,2,1,0}}; do
+    if which "$clangfmt" &>/dev/null; then
+        FMT="$clangfmt"
+        break
+    fi
+done
+
+# Check if we found a working clang-format
+if [ -z "$FMT" ]; then
+    echo "failed to find clang-format"
+    exit 1
+fi
+
+# Check all of the arguments first to make sure they're all directories
+for dir in "$@"; do
+    if [ ! -d "${dir}" ]; then
+        echo "${dir} is not a directory"
+        usage
+    fi
+done
+
+# Find a dominating file, starting from a given directory and going up.
+find-dominating-file() {
+    if [ -r "$1"/"$2" ]; then
+        return 0
+    fi
+    if [ "$1" = "/" ]; then
+        return 1
+    fi
+    find-dominating-file "$(realpath "$1"/..)" "$2"
+    return $?
+}
+
+# Run clang-format -i on all of the things
+for dir in "$@"; do
+    pushd "${dir}" &>/dev/null
+    if ! find-dominating-file . .clang-format; then
+        echo "Failed to find dominating .clang-format starting at $PWD"
+        continue
+    fi
+    find . \
+         \( -name '*.c' \
+         -o -name '*.cc' \
+         -o -name '*.cpp' \
+         -o -name '*.h' \
+         -o -name '*.hh' \
+         -o -name '*.hpp' \) \
+         -exec "${FMT}" -i '{}' \;
+    popd &>/dev/null
+done