libre.fm scrobbling support

[chrismou]

Related to #4

libre.fm implement much of their API the same as last.fm - ie, Now Playing and Scrobbling requests are identical (aside from the API URL).

Note - I think libre.fm only have username/password authentication at the moment (needs confirmation) so if opting for oauth for last.fm, this may require writing a separate authentication process for them.

Depends on #3 for somewhere to put the options