Add formatting script and support

.clang-format

+---
+Language:        Cpp
+BasedOnStyle:  Google
+KeepEmptyLinesAtTheStartOfBlocks: true
+PenaltyBreakAssignment: 2
+...

format.sh

+#!/bin/bash
+
+# Clang format command, can be overridden using CLANG_FORMAT_CMD.
+# We currrently use version 5.0 so any overrides should provide that.
+clang=${CLANG_FORMAT_CMD:="clang-format-5.0"}
+
+# Formatting command
+cmd="$clang -style=file $(git ls-files | grep '\.[ch]$')"
+
+# Test if `clang-format-5.0` works
+command -v $clang > /dev/null
+if [[ $? -ne 0 ]]
+then
+    echo "ERROR: cannot find $clang"
+    exit 1
+fi
+
+# Print the help
+function show_help {
+    echo -e "This script formats SWIFT according to Google style"
+    echo -e "  -h, --help \t Show this help"
+    echo -e "  -t, --test \t Test if SWIFT is well formatted"
+}
+
+# Parse arguments (based on https://stackoverflow.com/questions/192249)
+TEST=0
+while [[ $# -gt 0 ]]
+do
+    key="$1"
+
+    case $key in
+	# print the help and exit
+	-h|--help)
+	    show_help
+	    exit
+	    ;;
+	# check if the code is well formatted
+	-t|--test)
+	    TEST=1
+	    shift
+	    ;;
+	# unknown option
+	*)
+	    echo "Argument '$1' not implemented"
+	    show_help
+	    exit
+	    ;;
+    esac
+done
+
+# Run the required commands
+if [[ $TEST -eq 1 ]]
+then
+    # Note trapping the exit status from both commands in the pipe. Also note
+    # do not use -q in grep as that closes the pipe on first match and we get
+    # a SIGPIPE error.
+    echo "Testing if SWIFT is correctly formatted"
+    $cmd -output-replacements-xml | grep "<replacement " > /dev/null
+    status=("${PIPESTATUS[@]}")
+
+    #  Trap if first command failed. Note 141 is SIGPIPE, that happens when no
+    #  output
+    if [[ ${status[0]} -ne 0 ]]
+    then
+       echo "ERROR: $clang command failed"
+       exit 1
+    fi
+
+    # Check formatting
+    if [[ ${status[1]} -eq 0 ]]
+    then
+ 	echo "ERROR: needs formatting"
+ 	exit 1
+    else
+        echo "...is correctly formatted"
+    fi
+else
+    echo "Formatting SWIFT"
+    $cmd -i
+fi