frontlib improvements:
- Added README with overview documentation
- Improved code documentation/comments
- Added flib_gameconn_send_quit to gracefully exit a running game
- Changed the type of some size variables to size_t
- Fixed starting a mission/training sending the mission script like a multiplayer script
- Removed reference counters from flib_scheme and flib_map
- Removed INGAME state from netconn (there is no useful difference to ROOM state)
- Added extras/jnacontrol.c to warn when functions signatures used by Hedgeroid change
- Other small code improvements