feat(code-style): Add a script to automatically format all changed files

If executed inside the repository it will run the default Contiki
uncrustify script on all changed .c and .h file. This could be added
as a Git pre-commit hook. See http://git-scm.com/book/en/Customizing-Git-Git-Hooks
Merge pull request #375 from vsaw/tmp-uncrustify-changed

feat(code-style): Add a script to automatically format all changed files