Pulse Density Modulation

A cleaner, better way to do software power regulation, gives even power distribution and makes the most of the available time resolution. Also happens to be much more readable code :)
https://en.wikipedia.org/wiki/Pulse-density_modulation

Killed off extruders 4-6 for now because the UI makes no effort to support more than 2 at this time (using 3 has severe bugs , 4+ has no support whatsoever), so clearly nobody even uses 3. Patch to make UI work for 3 extruders coming up next!