add warning in README

Cleanup and improve documentation

Update Travis CI config

Update dependencies and Travis CI config

Update dependencies

Replace pipenv with pyenv + poetry

Code formatting (black)

Merge pull request #122 from jackdbd/pyup-scheduled-update-2018-07-30

Update tox from 3.0.0 to 3.1.2

Update sqlalchemy from 1.2.8 to 1.2.10

Update requests from 2.18.4 to 2.19.1

Update pyyaml from 3.12 to 3.13

Update pytest from 3.6.0 to 3.6.4

Update py from 1.5.3 to 1.5.4

Update psycopg2 from 2.7.4 to 2.7.5