Some unit test related proposals

While trying to figure out why the unit tests were failing for me and not you, I stumbled on the fact that Pandas 0.14 was the culprit. Running with pandas 0.13.1 worked fine. This is separately reported in issue #58.

First issue I had was that no encoding was specified for several files, so I added to all the files that were missing them.

Second thing was some python3 related syntax things, which I updated to be compatible with both Python2 and Python3. This was mainly the import of StringIO.

Third thing was going about making it work with Travis-CI. The build for my fork is here: [https://travis-ci.org/spacecowboy/lifelines](https://travis-ci.org/spacecowboy/lifelines). I realize you might not want to keep the change in requirements.txt, but it makes sure the tests pass at the moment. I also noted that you removed a travis-ci config in a previous commit so you might not want to keep this either.

But, one thing that was added due to the travis stuff is unit tests that are skipped if no DISPLAY-variable is available, which is the case on travis. This can be tested locally by _ssh localhost_ then running the tests.

Anyway, let me know if you want me to remove any of the changes.