removes travis-ci, updates documentation

Since we have no tests, I removed the travis-ci yml file and the build
status indicator in the README. I also added a few links the the
README (a link to readthedocs, the eventdata website, and tabari), and I
updated the contributing guidelines to reflect that fact that we have a
dev branch now.
Merge pull request #59 from zmjones/cleanup

removes travis-ci, updates documentation