implement serial protocol for touchscreen

[Austinpayne]

Protocol

CMD [PARAMS]\n

• CMD is cmd number (in hex)
• PARAMS depend on the command and are comma separated, i.e p1,p2,p3,...,pN

Need

• 0x0 status (params: 0=ok)
• 0x1 start new game (params: player_type=<human|ai>)
• 0x2 end turn
• 0x3 move piece (params: move (in LAN format, ex. e2e4))
• 0x4 promote pawn (need to figure out how chess-js handles this server side)
• 0x5 calibrate (photon initiated on new game, probably don't need to have user access)
• 0x6 end game (photon --> touchscreen, could also be touchscreen --> photon to indicate player wants to leave game)

Wow-factor

• 0x7 scan for wifi networks (see add ability to scan and configure wifi #1)
• 0x8 set wifi

Nice-to-have

• 0x9 get best move
• 0xA query existing games
• 0xB join existing game

[Austinpayne]

Seeing as this is shared by both photon and stm32 (no need to duplicate protocol parsing), this has been implemented here https://github.com/Austinpayne/chess-serial-protocol and is linked to stm32 as a submodule (see https://github.com/Austinpayne/steppers/tree/improve-uart-driver/Src) and implemented as a photon library for the photon