Lint the code

[ludwigschmidt]

Make sure our code mostly follows https://google.github.io/styleguide/cppguide.html and use their lint tool.

Ideally, we'd have a clear subset of the Google rules we adopt and a corresponding lint script (based on cpplint.py).

[ilyaraz]

Default settings for cpplint applied to HEAD return this: http://pastebin.com/BZH6MF6J Looks pretty sane to me, but we may want to make it stricter.