The iSerial descriptor now holds the firmware version number.  This is
1.0.0 since I don't expect any major API changes any time soon.  The USB
descriptors have been documented in docs/console_config.md so there
will be no questions as to how to identify the devices and what their
"serial numbers" mean.

As the name suggests, it clears all the flags in the configuration
buffer.  This provides a way to easily set all the flags to a known
state, which is nice for implementing libraries that configure PD Buddy
Sink devices.

It's very important to document the format in which configuration is
printed, since being able to reliably read the configuration is
essential to implementing configuration GUIs.  Now it's documented, and
the format is considered stable.

Now there's a docs/ directory for storing our documentation in!