Add support for Travis and Coveralls in a future-compatible way

This pull request is an alternative to yhat/ggplot#45. The main differences are that we fully embrace `setuptools` and `pip`, which are what most people use for package management these days, instead of trying to get by with `distutils`. According to [PEP 453](www.python.org/dev/peps/pep-0453/), `pip` will be included with Python starting on November 20th, and all official documentation will be updated to recommend using that instead of distutils.

Like yhat/ggplot#45, this PR also adds support for using Travis and Coveralls for automatic unit testing and coverage information. We greatly simplify the Travis installation by using conda to install the latest binary versions of all requirements.