Code Style: Add uncrustify config and helper scripts

This pull request adds a configuration and helper scripts for the [uncrustify](http://uncrustify.sourceforge.net/) code beautifier.

With these additions, the `tools` directory would start containing lots of code-style related files, so we create a new subdir `code-style` and we place everything therein, including existing GNU indent-related files.

Due to its very high configurability, uncrustify achieves a much better match of the Contiki style than GNU indent. We still don't have a silver bullet, some corner cases will get formatted incorrectly and will require developer intervention but all the basics work fine.

The wiki will need changed to reflect this change. I shall do so once/if this pull has been merged in and I'll also document cases where uncrustify gets it wrong.