Pulled some shared code into a generic method for testing TimedSemaphores to
clean up the module. Started the tests for the LimitRequests decorator.
Test for library.LimitRequests completed and the class has been created.
All tests pass.
Modifications to query.musicbrainz complete. Backoff is no longer used.
Changed reference to Backoff in test_Musicbrainz to change the LimitRequests
delay instead of the Backoff delay. All tests pass.
Removed Backoff as it is no longer used.