routes.rb-like targets for events

Add capability to specify the target for an event in a fashion similar
to the one used in routes.rb, e.g. "product#new_product". Added
examples to event_map_spec to test new functionality
Extracted validate_xxx_options to a separate TargetValidator class which can be reused fro other parts of the code. Added spec for TargetValidator.
Update README.md

Added explanation how to use the new syntax
Merge pull request #41 from nessche/routes-like-event-targets

routes.rb-like targets for events