(Thanks iquizzle)

Diffed and merged, preserving my updates

Reviert previous change of #if BLAH_PIN > 0 to #if defined(BLAH_PIN) &&
BLAH_PIN > -1. Unfortunately some times pin 0 is used. For my sins I've
gone through and replaced all unsafe checks of #if BLAH_PIN > -1 with
the safe version.

Add new 'callback' edit-menu types that call a function after the edit is done. Use this to display and edit Ki and Kd correctly (removing the scaling first and reapplying it after). Also use it to reset maximum stepwise acceleration rates, after updating mm/s^2 rates via menus. (Previously, changes did nothing to affect planner unless saved back to EEPROM, and the machine reset).

Add calls to updatePID() so that PID loop uses updated values whether set by gcode (it already did this), or by restoring defaults, or loading from EEPROM (it didn't do those last two). Similarly, update the maximum step/s^2 accel rates when the mm/s^2 values are changed - whether by menu edits, restore defaults, or EEPROM read.

Refactor the acceleration rate update logic, and the PID scaling logic, into new functions that can be called from wherever, including the callbacks.

Add menu items to allow the z jerk and e jerk to be viewed/edited in the Control->Motion menu, as per xy jerk.

Conflicts:
	Marlin/language.h

Add a feature to run the cooling fan at full speed for a small period
(default 100ms) when first starting the fan.  Some fans wont reliably
start spinning at low power, and many fans have issue with the PWM at
low power.  However, once the fan starts spinning it can reliably be
set to a wide range of PWM values.

Always set the FAN PWM value in check_axes_activity() and always use
the value of the active move if a move is active.

Turning off the protection might be beneficial to those who want to do fast and long reversals.

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

Fixed small bug in arcs
M105 prints now actual_temp/target_temp

Included AD595 calibration options. (daid)

Split ramps1.3 in Sprinter like config and multiextruder config.

Added M221 extuder multiply factor.

Updated the Xsteps ... settings via the LCD menu

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>

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