Failing tests for throwing on invalid events/transitions
Fixes inadvertent event attribute error in common invalid tests
Use the test machine, not the example machine.

a.k.a. how about we test the right thing?
Throw when current state does not accept known event
Throw when attempting to send an unknown event
Update documentation for cases where `send` throws
Merge pull request #4 from repeatingbeats/invalids

Invalid events have undefined behavior