Documentation restructuring

Conflicts:
	README.md

Documentation directory

(For the SLOW_PWM_HEATERS option)

Fix grammar/typos in new Configuration.h option

Revert "issue 968 for dev branch"

(For the SLOW_PWM_HEATERS option)

Updated pins reference and servo support.

cross referenced between Rambo 1.1, 1.2, and 1.3

moved/renamed documentation stuff to top-level directory

406*406 pixels

Update Marlin Firmware URL

Some corrections and new features

Master

ramps do have power for the servos, the power comes from the power connector, not sure why this note was even made

Dev-Pull

ok

For cartesian bots, the X_AXIS is the real X movement and same for
Y_AXIS.
But for corexy bots, that is not true. The "X_AXIS" and "Y_AXIS" motors
(that should be named to A_AXIS
and B_AXIS) cannot be used for X and Y length, because A=X+Y and B=X-Y.
So we need to create other 2 "AXIS", named X_HEAD and Y_HEAD, meaning
the real displacement of the Head.
Having the real displacement of the head, we can calculate the total
movement length and apply the desired speed.