Travis integration

I have created a .travis.yml file which allows travis-ci to build cabot. Most of the commands are just taken from /bin/provision with a few travis specific changes to let the build pass on travis. [My build](https://travis-ci.org/bonniejools/cabot) is passing.

I've also [added a badge](https://github.com/bonniejools/cabot/tree/travis_integration) to the README to display the build status. It shows failing now because it's linked with the current arachnys build which doesn't have a travis build file.