Add to Travis-CI

[athanclark]

@zaquest Hey there, I was going to add this library to Travis-CI, but I don't have sufficient rights to do so. I think this ought to be consistently monitored; it's such a fundamental concept, I'd hate to see it go incompatible as time goes on.

Thanks!

[zaquest]

Hello. Added to travis-ci and commited build status badge to readme. Let me know if you need anything else.

[athanclark]

Thank you!