Support multiple 'from' states

According to https://github.com/jakesgordon/javascript-state-machine:
"If an event is allowed from multiple states, and always transitions to the same state, then simply provide an array of states in the from attribute of an event."

So the from property can be of type string or string[], so "any" is required here.
Merge pull request #1558 from balassy/patch-1

Support multiple 'from' states