Automatically Lint the source files

[mricherzhagen]

I think the cpplint script does a very good job of checking the source files and we should integrate it into our cmake workflow, so style-errors are noticed immediately and don't pile up.

this is the result on running python2 cpplint.py include/**/* src/**/* on our master branch at 466a378c9937c331dbcb345fc7d4787a2b1ee3e0.

Besides line-length and names in TODOs i find most of the findings very reasonable.

Your thoughts?

[Markus-Goetz]

Seems very reasonable, should be automatically done. Can you create a CMake target, like e.g.

make lint

[mricherzhagen]

I think using the https://github.com/tkruse/cpplint fork instead of the original version is a good idea, because it has Python2+3 support.