This allows PID_FUNCTIONAL_RANGE to use a maximum duty cycle higher
than PID_MAX. This is useful for powerful heaters to heat quickly in
bang-bang mode, but use a lower duty cycle that is easier to stabilize
in PID mode.

Conflicts:

	Marlin/Configuration.h

see https://github.com/ErikZalm/Marlin/issues/148

Changed SLOWDOWN. IF this does not work ok OLD_SLOWDOWN is the old algo.

Moved the PID_dT in the Ki and Kd calculation from the configuration.h to temperature.cpp

M303 Starts autotune. Wait till the Kp Ki and Kd constants are printed.
Put these values in Configuration.h

The code to ignore the "bad thermistor reading failsafe"
suicide function depends on the existing of the PS_ON pin
feature.  But in some boards this shouldn't be the case
Fix this by adding an explicit definition to make our
intentions more clear and separable.

ON GEN7 there is no temperature reading when power is off.. so Marlin
would kill itself. There seems to be an update from "Traumflug" on GEN7
using standby VCC for thermistors.

Needs some work to remove the blocking in read max6675.

advance and ultipanel not any more in default config

This reverts commit 651cde8b98.

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.