Fixed an issue with multiple parameters to the string interpolation

This fixes #10 (again)
Added a toString method to events, so they can be debugged nicely

This fixes #24
Added errorHandler to qvc fetching constraings and executing command/query. Exception message is sent to the errorHandler

This fixes #21
Merge branch '24_EventToString'
Merge branch '10_stringInterpolationErrors'
Release 0.2.11