[0.2.dev9] Small fixes and doc improvements

[smmaurer]

This is a PR of small changes that have been sitting around for a while:

• adds a CHANGELOG.md :tada:
• adds a contribution guide
• adds some more info the the readme
• simplifies the setup script to just use setuptools
• refactors the column name check in MergedChoiceTable per https://github.com/UDST/choicemodels/pull/54#discussion_r241126449

I'm planning to update the Sphinx documentation and then release this as 0.2, since there's a lot of new functionality in the choice table and simulation tools.

Versioning

This PR is 0.2.dev9

[coveralls]

Coverage decreased (-0.07%) to 75.113% when pulling dbbb49f287501d35d03b0c914f33cb5f9459f5dc on doc-improvements into 4fb81099147a4efa83e98807c3311f29a09d7ef5 on master.