Add to_fpe2() method. Comment fixes.

- to_fpe2() for converting fan RPM for writes
- Rename fpe2() -> from_fpe2()
Improved setFanRPM() which is now setFanMinRPM()

- Misinterpreted min fan SMC key (see method description). Corrected safety
  check
- Add fan safe SMC keys
- Better param name for fan methods
Merge branch 'set-min-fan'