Install ruby package, don't install docs for gems.

Fixes #8
Create rails playbook

- Install gem package and install rails gem.
- Install rails globally as ansible default is user.

Fixes #10
Closes #39
Add PgSQL APT repo and install PostgreSQL 9.3
Change pg_hba and restart postgresql.
Install ruby-dev, build-essential, ruby-pg, libp5 and libpq-dev in
given order.
Install ruby package, don't install docs for gems.