Release v2.0-pre1.

Finalized general board layout.

Each tube gets its own current feedback loop. Controlled by the shift registers and the DAC. Tube current can be individually adjusted (8-bit DAC) between 0 ~ 10.6 mA.

What worked:

- Power supplies (180V, 5V, 3.3V)

- Microcontroller

- Real time clock

- Level shifter

- DAC

- Shift registers

- Analog multiplexers

What didn't work:

- Current control

I messed up the footprint for the BJTs.