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

Found a couple of unused variables, that I commented.
Tried to solve the program memory warning message, and failed.

Might be replaced by something more clever, e.g. by erik, and does not yet support the second extruder or the bed.
its kind of not so cool, because you need 6 more ints.
Maybe isheating() should use the degrees directly, as it is not used in time-critical anyways.
Then it would be much easier. to have the offsets without additional variables.

This reverts commit 8bcdb9f5f0.