Updates for GitHub issues #3 and #4

Closes #3 
Closes #4 

Also added in signal names for debug purposes
Yep, with one thing possibly missing: have the completion block `nil` out the query.

This might not be strictly necessary, but since the disposable also gets called in the cases of completion or error, making the query `nil` ensures there's no weirdness by calling `-stopQuery:` on an already completed query.