Use Ruby 2.0.0 and Rubygems 2.0.3

These are the defaults on Heroku now.
Remove trailing slash from PATH entry.

This is really just an aesthetic thing, but it looks odd when `which ruby`
returns '/opt/ruby/bin//ruby'
Move Postgres user creation later.

This needs to be sometime after Postgres starts. Previously it was before
Postgres started.
Merge pull request #27 from georgebrock/master

Ruby 2.0.0, and some minor fixes