formatspecs, making for much cleaner code. Reformatted everything.
This actually happened in multiple steps but then I corrupted my local
repository and I had to recover from the working tree.
The addition of the new tcsetattr call fixes a problem where interrupting
fluxengine during a flux read will leave data in the device and/or Linux's
serial buffers, so that the next invocation of fluxengine will fail similar
to
```
Error: command returned garbage (0x27 != 0x0 with status 0x31)
```
(the specific value differs because it's actually flux data)
Merely changing the existing tcsetattr call to specify TCSAFLUSH was not
enough; moving it after the 200ms pause seems to be enough.
Note that it doesn't seem feasible in our USB stack to make DTR reset
the device, since that would take down the USB stack and require a fresh
USB connection.
The addition of the special case for `rlen == 0` in read is for when the
GW-compatible board is reset or crashes and usb-disconnects during a
reading operation. Without this change, fluxengine spins forever at 100%
of a CPU, repeating a read(). After the change, this will cause
the host computer to print messages like:
```
2.1: 200 ms in 68928 bytes
3.0: Error: serial read returned no data (device removed?)
```
and exit.
I only tested these changes on Linux (Debian with kernel 5.10) and in
particular I don't know if/how it will work on a Mac.
2) fix gw readflux command (should be 8 bytes long but was packed as 10)
3) add support for non-gw VID/PID (generic serial port that is gw compatible)
4) manually set/clear DTR on serial port devices - this seems to be essential for tinyusb/arduino CDC
not tested with a gw but ought not to have broken anything!
