Finite state machine notes.
- https://www.weiyun.com/disk/folder/4efd4705bdef0050778b0eb86ab313de
- https://github.com/jakesgordon/javascript-state-machine
- http://www.ruanyifeng.com/blog/2013/09/finite-state_machine_for_javascript.html
- https://css-tricks.com/finite-state-machines-with-react/
- https://css-tricks.com/robust-react-user-interfaces-with-finite-state-machines/
- https://github.com/yhanwen/fsm