Version 0.6.0

Version 0.5.3

Version 0.5.2

Version 0.5.1

Version 0.5.0

Version 0.4.0

Version 0.3.1

Version 0.3.0

Version 0.2.0

Preliminary traunch of features

1. Add users and databases.
2. Drop users and databases.
3. List users and databases.

Also pull together the layout for the interface.

1. `command` objects do the work.
2. `prompt` objects are the user interaction.
3. `Pgchief::User` and `Pgchief::Database` are helper classes to interface with PG.

Write initial specs against commands. Still need to land on how to run integration
tests against the `TTY::Prompt`-led user-flows.

Still plenty of room for refactoring, polish, and improvement.