TST: Travis CI for automated node testing

To enable Travis CI, simply register on their site, flip the ON switch for caolan/highland and then change the README.md from eshao/highland to caolan/highland. 

I also looked into two solutions for automated cross-browser testing. Both zuul and testling generally require mocha or tape as the test producer for *drop-in* integration. If we put a bit of work into it, I guess we can make it work with nodeunit. However, I think we should do it as proving which browser versions we're compatible with is better than simply saying we're "browser compatible."