Docs: State Machine Diagrams

[ForbesLindesay]

I was looking to better understand the state transitions for the Saxes parser, so I created state machine diagrams covering all the states. Not sure if it would be useful to others/worth including as documentation, but in case it is, feel free to use: https://gist.github.com/ForbesLindesay/f30b317013b9851149178c9f30993f6c

I've attempted to document all state transitions that don't result in a call to this.fail.