Travis CI

I've added a [Travis CI](http://travis-ci.org) build configuration file. You should sign up and turn on automatic building of [coolwanglu/pdf2htmlEX](https://github.com/coolwanglu/pdf2htmlEX).

I've already signed up [my fork of pdf2htmlEX on Travis CI](https://travis-ci.org/jahewson/pdf2htmlEX)