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

The README now outlines the features of the PD Buddy Firmware.

A bit of documentation was added to main.c, along with renaming the
pd_buddy() function to sink().

The repositories have been moved to the PD Buddy organization.

Now that there's a decent GUI, we can at least mention that it exists in
the README.  It's good to make people aware of their options, you know?

Also, I got tired of the inline URLs, so I changed the links to be of
the footnote type.  It's much nicer looking e.g. in the list of firmware
flashing programs.

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.

When flashing with OpenOCD, you should use the .elf image, not the .bin.