Format README.md with subsections

Having actual section headers instead of just bold text makes those parts of the document individually linkable.

Fix bugs in Extruder Runout Prevention, including DAMAGING HEAD CRASH

This seems to defeat the purpose of previous_millis_cmd, preventing the
time elapsed from previous_millis_cmd from ever reaching
max_inactive_time or stepper_inactive_time while the heat was on.

Fixes a bug in the Extruder Runout Prevention feature that caused the
extruder to move back to “current_position” after a move if it was
activated while the move was in progress. For long home moves (which
are longer than the dimensions of the machine’s working area), this
would cause the machine to crash into the far end of its travel after
homing. This usually occurred on the Z axis, which could result in
damage to the machine if you don’t hit the reset button in time.

Update ConfigurationStore.cpp

Unable to compile if ENABLE_AUTO_BED_LEVELING is not set (not set by default).

Add Ultiboard2 electronics. With PWM current settings. For the few people that have this new board as experiment in their UM-Original.

Improvements to the auto bed leveling feature

Conflicts:
	Marlin/Configuration.h
	Marlin/Marlin_main.cpp

Correct missing parameter from last upmerge

Signed-off-by: Joseivaldo Benito Junior <jrbenito@benito.qsl.br>

Update Delta example files

Signed-off-by: Joseivaldo Benito Junior <jrbenito@benito.qsl.br>

Minor improvements for encoder configuration, LCD entry for PSU controll and thermistor pins on RAMPS

Revert "Made numbering of heat bed thermistor more logical as D8 is bed, D9 is Extruder 2 and D10 is Extruder 1, so T0 should be E1, T1 E1 and T2 bed to be sequential as MOSFET-Outputs"

This reverts commit b7eadb9f.

Added new board

Z and Y dual stepper drivers error

if you try to enable Z_DUAL_STEPPER_DRIVERS the error "You cannot have dual drivers for both Y and Z" shows even if you don't have defined Y_DUAL_STEPPER_DRIVERS and don't let you compile the firmware

to solve this problem i change this line:

#ifdef Z_DUAL_STEPPER_DRIVERS && Y_DUAL_STEPPER_DRIVERS

to:

#if defined (Z_DUAL_STEPPER_DRIVERS) && defined (Y_DUAL_STEPPER_DRIVERS)

now the error only show if you define both Z_DUAL_STEPPER_DRIVERS and Y_DUAL_STEPPER_DRIVERS

Added posibility to set ENCODER_STEPS_PER_MENU_ITEM in Configuration.h like ENCODER_PULSES_PER_STEP as it depends on it for usability

Made numbering of heat bed thermistor more logical as D8 is bed, D9 is Extruder 2 and D10 is Extruder 1, so T0 should be E1, T1 E1 and T2 bed to be sequential as MOSFET-Outputs

Added support for Cheaptronic v1 electronic

The code for the LSQ solver (qr_solve) is copyrighted by John Burkardt and released under LGPL here:
http://people.sc.fsu.edu/~%20jburkardt/c_src/qr_solve/qr_solve.html
(see qr_solve.cpp for further copyright information)

Removed the calculation of the inverse matrix since the rotation matrix is orthogonal, therefore inverted == transposed.
Much simpler and mathematically robust.

In some cases the Bed Heater FET heats up more then stepper drivers, so
this change add the bed monitoring to the controller fan. As soon as the
bed heater is turned on, the controller fan will run as well.

Recommended for those who are using the Z Probe for Z Homing (as
Z-Endstop)

This feature has two changes:

1) Allow user to choose where the Z Probe will touch the bed when homing
all axis together (G28) by setting below defines:

Z_SAFE_HOMING_X_POINT
Z_SAFE_HOMING_Y_POINT

2) Prevents the user to perform Z Axis Homing when the Z Probe is
outsite bed.

In previous version, even with PWM = 127, the system turns the FET off
and then on in the next cycle. This bevavior may increase the FET heat
dissipation.
It was fixed keeping the FET always On when PWM=127.

This allows a hot end with two heaters and a FET for each heater. This is useful if the FET is not capable of heating two heaters.