README: convert py3.7 specific steps into generic py3 steps, and list oldest Debian and Ubuntu versions supported

README: amaranth depends on py3.8, so follow suit

README: swap 'setup.py' for 'pip install -e'

CI: enable builds for merge queue.

applet.interface.spi_controller: convert to native amaranth Addresses a bunch of items from #150.

README: add notice for crowdsupply buyers.

applet.program.stusb4500_nvm: Import new applet to program STUSB4500 NVM Signed-off-by: Sylvain Munaut

software: migrate from `crcmod` to `crc`. The `crc` package is maintained and does not have problematic native dependencies.

applet.interface.jtag_svf: ignore TRST OFF when TRST# not present Some SVF producers (like Xilinx impact) emit a TRST OFF command as part of the initialization. This has no effect other than bringing the system to the default state, so ignoring it when there is no TRST# pin is harmless. Likewise, ignore TRST Z in this case.

applet.display.hd44780: convert to native amaranth Addresses `display.hd44780` item from #150. Includes some trivial gateware improvements.