Configuration.h, pins.h: Add MOTHERBOARD 84 for Teensy++2.0
Merge pull request #941 from drf5n/teensypp2

Configuration.h, pins.h: Add MOTHERBOARD 84 for Teensy++2.0
Fixed a comment in the planner
Merge pull request #946 from Jnesselr/jnesselr/plannerdoc

Fixed a comment in the planner
Add switch unused feeder(s) off

Having the non-active feeder motors powered on all the time is not
necessary. A feature to deactivate the unused feeder motors has been
implemented. The feature is enabled on default but can be switched off
in the configuration.
renaming the disable inactive extruder feature
Merge pull request #947 from Dim3nsioneer/Marlin_v1

Add feature 'switch unused feeder(s) off'
M30 response is missing linefeed, "ok" therefore not on own line

This leads to the command not being acknowledged properly
by the firmware, leading to consecutive issues in host software
waiting for an acknowledgement.
Merge pull request #949 from foosel/fix/M30_clearToSend_bug

M30 response is missing linefeed, "ok" therefore not on own line
Added thermistor table for the 500C thermistor shipped with the Pico hot end.
Merge pull request #955 from gregington/pico-thermistor

Added thermistor table for the 500C thermistor shipped with the Pico hotend
Fixed stop print LCD function on M104
Inverted state logic for forced_heating_stop variable
Changed the type of variable to bool, the name to "cancel_heatup", flags implementation and added this fix to M190 gcode too.
Merge pull request #965 from bq/forced_heating_stop

Fixed stop print LCD function on M104
Add "Thermal Runaway Protection" feature

This is a feature to protect your printer from burn up in flames if it
has a thermistor coming off place (this happened to a friend of mine
recently and motivated me writing this feature).

The issue: If a thermistor come off, it will read a lower temperature
than actual. The system will turn the heater on forever, burning up the
filament and anything
else around.

After the temperature reaches the target for the first time, this
feature will start measuring for how long the current temperature stays
below the target minus _HYSTERESIS (set_temperature -
THERMAL_RUNAWAY_PROTECTION_HYSTERESIS).

If it stays longer than _PERIOD, it means the thermistor temperature
cannot catch up with the target, so something *may be* wrong. Then, to
be on the safe side, the system will he halt.

Bear in mind the count down will just start AFTER the first time the
thermistor temperature is over the target, so you will have no problem
if your extruder heater takes 2 minutes to hit the target on heating.
Changed the declaration of the variable to Marlin_main.cpp to fix issue on commit #965
Merge pull request #989 from bq/cancel_heatup

Changed the declaration of the variable "cancel_heatup" to Marlin_main.cpp to fix issue on commit #965