Continued implementation of safety switches module.
Movement is now safety switch aware.
There is much to do.
Better compiler error when printf is referenced.
Disambiguated the E report.
Comment only.
Declared safety_private fields volatile.
Cleaned up engine.c, reinstated F_SU fault.
Updated in-memory tracing to print small integers as atoms.
Fixed serial driver bugs.
Lasers now tested and working in all modes.