Add test framework with Travis CI and Coveralls

Re:
https://github.com/unitedstates/congress-legislators/pull/176
https://github.com/unitedstates/congress/issues/118

To get you started, here's a test framework using Travis CI and Coveralls coverage. Both Travis CI and Coveralls are free for open source. They give reports like this (from my fork):
https://travis-ci.org/hugovk/congress-legislators
https://coveralls.io/r/hugovk/congress-legislators

`.travis.yml` defines the build environments and commands. It runs the sample `test_utils.py` with coverage, and sends the report to Coveralls. For good measure, pep8 and pyflakes are run at the end of the CI build.

Before accepting the PR, go to Travis CI and Coveralls and enable this repo. That way'll you'll get a report for the merge.