Invalid medthod signature when using authorise method

Hello

Creating the method signature fails when scrobbling a track without an MBID or when using the `authorise` method.

 - When scrobbling a track without an MBID, an empty parameter was added to `requestParams` but it was omitted in the method signature resulting in an invalid signature for the API request.
 - When using the `authorise` method, a call to "auth.getsession" was made in the `validateToken` method. This works, however, the LastFM API requires the method name to be case-sensitive in the method signature resulting in an invalid method signature. The "s" in "getsession" should be a capital "S" i.e. "getSession".

I hope this helps. Thank you very much.