simulator/heater_sim.c: Add notes that the heater isn't implemented in the simulator.
dda_maths.h: Add comment on units of C0.
dda_lookahead.c: Eliminate debug crossF uninitialized variable compile warning.

Fix:
  dda_lookahead.c:327:17: warning: 'crossF' may be used uninitialized in this function [-Wmaybe-uninitialized]
       sersendf_P(PSTR("Initial crossing speed: %lu\n"), crossF);
                 ^
config.default.h: Add DEBUG_LED_PIN to the pinout section.
arduino_32U4.h: remove definition of DEBUG_LED_PIN from here, leaving it optional in config.h.
gcode_process.c: Add comment on units of P - M130 , I - M131, and D M132 parameters.
heater.*:Adjust DEFINE_HEATER macro to provide PID values.
heater.c: Add units comments and sum the PID in consistent units, changing internal kP,kI,kD meanings.
config.teensypp.h: Add note on compiling from the command line
heater.c: Parse PID table -Ki as a raw value.
heater.c, heater.h, gcode_process.c: Replace hard-coded PID I_LIM with adaptive anti-windup logic.
heater.c: Add some PID units notes.
heater.c: interpret -tD as kD.  config.teensypp.h: Switch to PID table.
heater.*: Remove PID I-limit traces.
heater.c:initialize heater_i to 0.
heater.c: Apply *16 factor to integral accumulator backcalculation (1Cs=16qCqs).
config.teensypp.h: Update some comments, and align with my machine.
Move the PID_SCALE_[PID] into heater.h from config.*, and apply them.  if -kP then Kd=Ki=0.
heater.c:Comments.  config.teensypp.h heater.c: move PID_SCALE_[PID] constants to header.
heater.h: Cast the PID_SCALE_? types to int32_t

Conflicts:
	heater.h
heater.*: change and doucment units for PID parameters