Last.fm Now Playing module

This pull request adds the module `bones.modules.lastfm.Lastfm`, which adds a "now playing" feature for last.fm users.

Triggers:
`+lastfm [-rd] [nickname]`
~~~~
Flags (Optional):
   -r nickname:
   Register the provided Last.fm username to your nickname

   -d:
   Remove a registered last.fm account from your nickname

Arguments:
   nickname (Optional):
   If provided, +lastfm will check the status of the account connected to the specified nickname.
~~~~

Database structure creation will come in a later version, for now you'll have to create the tables by hand by looking at the objects in the `bones.modules.lastfm.Lastfm` module.

PostgreSQL is the only officially supported DBMS.