Add auto-formatter to Flycheck

[swsnr]

Add maint/format.el and a corresponding make format which formats all sources according to our style guide as far as possible. It should

• reindent the buffer (requires loading unfortunately)
• cleanup whitespace to remove tabs, trailing spaces, etc.
• further ideas?

We should also replace the test that checks for proper indentation with a test that checks for proper formatting by applying the formatter to a file and checking for modifications.

[manuel-uberti]

Very nice idea.

Could there be naming conventions (i.e.: a checker's name) to check?

[swsnr]

@manuel-uberti Maybe, but not within the scope of this ticket.

[manuel-uberti]

@lunaryorn ok. Then reidenting the buffer and cleaning up whitespaces/tabs should be enough.