[0.2.dev10] More release prep

[smmaurer]

This is another PR of miscellaneous updates:

• complete overhaul of the documentation :tada: (currently hosted at https://choicemodels.readthedocs.io, soon moving to https://docs.udst.org/projects/choicemodels)
• adds a Python 3.7 build to Travis (currently allowed to fail because dependencies won't install)
• streamlines the Travis build script to use standard Python images instead of Anaconda, which reduces the CI runtime by more than 50%
• moves the choicemodels.tools.distancematrix functions directly into choicemodels.tools (their names are clear and this is still a small library -- seems easier for users)

Versioning

0.2.dev10

[coveralls]

Coverage increased (+0.04%) to 75.151% when pulling 3fd1c468925dc99799695ccf81b69790c56694ec on docs-work into c2f8e658086c4fa6fd7148ba3a36ce829d5e0ca9 on master.