Some general modernizations and Travis-CI tweaks

Mostly I wanted to test the travis setup was working and got carried away... hopefully you guys like these changes because we don't need to be so old school with the straight up text files now that we aren't in the server repository.

You can see what it looks like on my fork:
README.md https://github.com/TylerBrock/mongo-cxx-driver/blob/legacy/README.md
CONTRIBUTING.md https://github.com/TylerBrock/mongo-cxx-driver/blob/legacy/CONTRIBUTING.md

Also, if you call the contributors files CONTRIBUTING.md you get nice looking markdown and the nice feature described here: https://github.com/blog/1184-contributing-guidelines