Command line arguments

This code can be merged safely. The Command Line interface is here, we will need to provide some more arguments, that's for sure, but at least we have a safe starting point.

@dchilot: I had to slightly modify the .travis.yml file since the clang build was always failing. I know you have fixed it (I know also HOW you fixed it), I just hope you won't have a bad time merging this on your side.

For all the others: feel free to add your emails to the .travis.yml file