Another big ChibiOS update, this time to the first stable release in the
18.2.x series.  This time a few pieces of API that the firmware and
library used were renamed, so there were some changes that had to be
made there.  The build system is nicer now, as the included makefiles
add paths to the necessary variables so the main Makefile is much less
verbose in a few places.

Technically I updated to a development version somewhere between 17.6.3
and 17.6.4, but I don't doubt its stability.

This is a good update because I'd like users of the library to be
confident that it works with the latest version of ChibiOS.
Interestingly, none of the changes I made were in the library code, so
it did before, but now I know for sure.

I'm unclear as to whether I can now get rid of the INT_N thread in favor
of a pin interrupt.  I'll have to see if I can, or if that will have to
wait for still more ChibiOS updates.

The command shell is based on the ChibiOS-provided one, but modified to
not run in a new thread and generally be a bit simpler, while also
having PD Buddy branding.  The storage functions work with the STM32
flash registers directly, taking over the last page of flash.  A new
linker script is used to ensure that program code can't end up using
that page.  The DPM has been updated to use the saved settings rather
than hardcoded ones.  Now what's needed is real commands for editing the
configuration.

Added commands to edit configuration

We now have commands to load the current settings into RAM, edit the
settings in RAM, and write them back to flash.  The only settings
currently supported are current and fixed voltage, because the rest of
the code doesn't support GiveBack or variable/battery PDOs yet.

Short help messages were added for each command.  Nothing too exciting,
but it should be a great help for someone poking around in the PD Buddy
Sink configuration shell for the first time.

Wrote new usage information for the firmware

Now that we have a command shell, the README should indicate how to use
it.

The original, unmodified portions of ChibiOS retain their original
copyright notices, for the portions of code to which they still apply.

Based on the RT-STM32F072-DISCOVERY demo from ChibiOS/demos/STM32.  The
board definition was made with the Eclipse plugin, and is based on the
ST_STM32F072B_DISCOVERY board definition from ChibiOS/os/hal/boards.