Ported to SQLAlchemy

Dropped MongoDB as main datastore, ported to SQLAlchemy, enabling more
datastores.
Added in a few missing requirements.

Included psycopg2 and pysqlite to make deploying against postgres and
sqlite easier.
Removed top level /i/ or /u/ in URL routes.
Changed DB and Redis config vars to direct reads

No longer reads one var to point at another.
Removed pysqlite requirement

Doesn't want to build on heroku right now.
Added Gunicorn requirement.
Big README.md Rewrite