Add true state machines

[denis-stepanov]

The application makes use of state machines, as described in operation manual. They are loosely emulated in the code with manual coding. [As if we have not got enough dependencies :-)~ , ] it would make sense to make use of some true state machine framework. Top 3 of candidates:

• arduino-fsm
• Automaton
• StateMachine

[denis-stepanov]

Trouble here is that the current application already balances at the limit of RAM available. Bringing new libraries would require careful watching for memory.