Coding style configurations

Users want to know whether coala will enforce a specific widely used style guideline.

We should have a documentation about each of these style guidelines, and tell them which bears will do the job.
Currently most of the bears are not preset style oriented, so the documentation page would need to describe a sample `.coafile` which achieves roughly what the guideline recommends.

e.g. read one of the guides at https://github.com/google/styleguide , find an existing codebase that uses the style guide , and try to configure coala bears to check that codebase without recommending bad changes to the codebase.