Updates for GitHub issues #3 and #4

Closes #3 
Closes #4 

Also added in signal names for debug purposes
:+1: 

So I had a quick look, and have another suggestion. You may want `nil` the query at the beginning of the completion block, before calling `-sendCompleted:` or `-sendError:`, because those methods both dispose the disposable. Maybe it's perfectly ok to call `-stopQuery:` on a query that has already completed, but it's not documented so I would suggest avoiding it, as a defensive approach.