Add format options for path and changed files based on git diff

[ElectricRCAircraftGuy]

Options should include a list of files or dirs, or a commit range of changed files.

See also my answer here: https://stackoverflow.com/questions/30905086/git-list-of-all-changed-but-not-deleted-files-in-a-commit/66649684#66649684.

The below func works only on filenames which have no spaces or special bash chars. So, make it work with spaces too!

To make it handle these chars, it will require using git diff --name-only -z or something. See my answer here: https://stackoverflow.com/questions/28109520/how-to-cope-with-spaces-in-file-names-when-iterating-results-from-git-diff-nam/62853776#62853776

Example:

gs_format_code() {
    files="$(git diff --name-only --diff-filter=d $1 $2)"
    echo "Manually formatting just these files:"
    echo "$files"
    clang-format --verbose -i --style=file $files
}