Add a Table to hold the GPG Keys of users
Make a valid username start and end with an alphanumeric
Add more constraints on valid values into the DB Schema
Update the models for accounts to make transition easier
Rename convert_pypi.sql to conversion/user_accounts.sql

This more accurately reflects the fact that there is going to be
multiple of these scripts whose purpose will be converting the
schema from PyPI to Warehouse.
Fully Convert the PyPI users table into the Warehouse accounts_user
Update comment to accurately reflect code
Merge pull request #23 from dstufft/user-account-parity

Finish Modeling User Accounts