Setting up Travis-CI

Should enable automatic builds/tests using travis: https://travis-ci.org/spotify/annoy/

Lots of small changes, see commit.

Unfortunately I can't get this working with Python 3. I get an issue: undefined symbol: PyClass_Type (see https://travis-ci.org/spotify/annoy/jobs/40478879 for more info). It seems like linking against boost_python with Python 2.7, but I haven't been able to figure out how to get boost_python4 to be installed