TST: Run Travis CI tests on both release and master versions of pandas
TST: Environment variable in .travis.yml needs to be preceeded by dollar sign
TST: Add Cython to requirements (needed to build pandas)
TST: Try direct install of pandas in .travis.yml
BUG: Use generic **kwargs to catch changes in pandas method APIs
Merge pull request #32 from kjordahl/feature/travis-pandas-versions

Run Travis CI tests on multiple pandas versions