(so 0 to 255 now goes from 0.00V to 5.10V)

(users complained, and extended simple UI probably needs to be off by
 default in all factory builds anyway)

Before this branch, `voltage` was 6 bits: Volts * 10
A couple patches ago, I upgraded it to 16 bits: 65535 * Volts / 10.24
That costs too much extra ROM on attiny85 though, for extra precision
it doesn't even use... so I switched back to an 8-bit value.  It's still
more precise than before though: Volts * 40
... and battcheck displays an extra digit now, on devices with ROM for it.
... and battcheck waits a second to get a more accurate measurement
    before displaying the first value.  It has *much* less variation
    between first and later readings now.

Also:
- got t1616 builds working again (tested fc13 and thefreeman-boost-fwaa)
- upgraded t1616 voltage and temp to 12-bit (10 bits + 4x oversampling)
- removed expensive temp conversion from t1616 ADC interrupt
- recalibrated t1616 bogomips again; runs faster after interrupt fix
- increased t1616 internal VDD measurement resolution by 36% (1.5V Vref, not 1.1V)
- fixed sloppy setting of Vref bits

I still need to test / update other t1616 builds,
and fix all the t85 + t1634 code and build targets.

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

and updated other scripts and files accordingly

(still need to update file contents afterward,
 but doing it in a separate commit so git can detect renames easier)

(also modified the build scripts to work with the new file structure)

(just moved files, didn't change the contents yet,
 and nothing will work without updating #includes and build scripts and stuff)