It had no minimum thermal stepdown defined, so it used MAX_7135 by default,
which was level 149/150 ... thus virtually no regulation.

I also made it easier to switch between internal and external temperature
sensors by just commenting out a few lines in the hwdef.h.

(the MCU's internal sensor works too, but external is a bit better I guess?)

- upgraded to DSM: lower lows, *much* smoother ramp
- made lows more efficient with underclocking
- fixed party strobe being too blurry
- calibrated UI speed / bogomips multiplier
- added readme to document this hardware's multiple quirks

Phew, that's a lot of changes!  And there's still a lot more to do...