gateware.uart: support words longer than 8-bits It seems that the shift register was being truncated to 8-bits regardless of the requested word size, since the `data_bits` attribute was introduced in 0f497e4a.

gateware.uart: convert to nmigen

applet.interface.uart: convert to nmigen

Switch CI from Travis to GitHub Actions.

firmware: fix ~ALERT interrupt handling The interrupt is level triggered on the FX2, so disable the handler until the ADC disengages it. It did somehow "work" without this fix, but the CPU was spending most of it's time entering the interrupt handler. Found by mistakenly not properly disengaging the ~ALERT line, then all USB comms broke. This doesn't happen with this commit.

firmware: implement initializing and reading alert limits for the INA233 With this firmware it is now possible to use regular "voltage" cli commands on revC2 to enable ports and read the sensed voltage back.

firmware: implement voltage reading for the INA233 move adc_reg_read()/_write() to util.c and rename to i2c_reg8_read()/_write() as they are used by both ADCs and can most probably also be used for other I2C peripherals.

firmware: rename adc file and functions to prepare supporting the INA233 ADC too

cli: coarsen --trace VCD timestamps to 10 ns. This speeds up dumb VCD viewers like sigrok that do work per sample rather than per edge by an order of magnitude at the cost of some non-accumulating loss of precision. Although unfortunate, sigrok is just far too slow to decode traces without this hack.

revC2: Generated gerber, bom and renderings. Additionally, the glasgow subdirectory README now contains information on how to generate the 3d renderings included in the glasgow repository.