Needs some work to remove the blocking in read max6675.

Added late z enable. (blddk request)
Only calculate look ahead if >2 moves in buffer.
Removed some FORCE_INLINE to save memory.

Signed-off-by: Erik van der Zalm <erik@vdzalm.eu>

advance and ultipanel not any more in default config

Soft PWM. (Sanguinololu can also have PID temperature control)
Interrupt save WRITE for addresses > 0x0FF

- The temperature control is pretty much complete
  (not sure what to do w/ autotemp though)
  Changed the pins assignment to clearly separate bed and extruder heaters
  and temp sensors, changed a bit how termistor tables are handled.
- The steppers control is rudimentary
  (only chanages what pins it uses depending on the active_extruder var,
   but that's enough for switching extruder in the start.gcode in the
   the profiles)
- Tested only w/ RAMPS 1.4