Move config out of source code and expect it to be defined in .env files

Closes #94

Code Review Checklist (to be filled out by reviewer)

[x] Description accurately reflects what changes are being made.
[x] Description explains why the changes are being made (or references an issue containing one).
[x] The PR appropriately sized.
[ ] New code has enough tests.
[x] New code has enough documentation to answer "how do I use it?" and "what does it do?".
[x] Existing documentation is up-to-date, if impacted.