Initial implementation of identi.ca support.

- requires oauth ~> 0.4.6 and a monkey-patched twitter_oauth
- implements a polling based approach to feeding new
  statuses to the user, as identi.ca does not have
  a streaming API
- also polls direct messages

There is an open pull request[1] for twitter_oauth that makes the
URLs configurable, but until this is merged and the gem updated, the
monkey-patch will be necessary.

[1] https://github.com/moomerman/twitter_oauth/pull/33