datapainter

IMHO the driver should use the new FIFO hal type for the data path so its just
a standard driver that presents hal pins to LinuxCNC.

Parts of the driver are much like a velocity mode stepgen except instead or outputting steps
it is outputting a data stream (either 1 bit or PWM) synced (phase locked) to position.
This position could br a linear axis for rastering or a calculated path length for drawing
on complex surfaces.

There are some tricky bits involving start/stop position synchronization
due to the fixed point limited range hardware breakpoints and floating
point position comparisons