With the VBUS symbol merged into the KiCad library, I no longer need to
use my own.  This commit changes the schematic to use the standard VBUS
symbol rather than a custom one.

In preparation for adding a second board (the programming jig) to this
repository, I've moved the PD Buddy Sink files to their own directory.

This is a major change!  Almost all the components have changed to
smaller versions, with 0603 and 0402 passives and a QFN microcontroller.
The board now has four layers, with internal layers used for VBUS and
GND.  The board now measures a mere 25×30 mm!  The SWD header and Boot
switch footprints have been moved to the bottom to help with this
shrinkage.  Two test points were added to the bottom as well to make it
possible to power the board without using the USB connector.  The
mounting holes are now slightly smaller (better sized for M3), and only
17 mm apart instead of the old 18 mm.

To sum up, everything is smaller and that's almost entirely a good
thing, except now it's not really possible to build one by hand.

It's a USB Type-C connector just like the one used in v0.1 and v0.2, but
with only SMT pins (except the fixing pins, of course).  They're
slightly cheaper and probably nicer for automated assembly, but
impossible to hand-solder.  That's okay though: where we're going, we
don't need hand-solderability.

That's the name they should have, since the board hasn't been called PD
Buddy since v0.1.

Google likes the name better this way.  Plus, it provides clear naming
for possible future PD Buddy products.

It was bidirectional on the Microcontroller sheet, which is wrong.  Now
it's input, like it should be.

I had the source and drain reversed—whoops.  After fixing it with an
X-Acto knife and some point-to-point wiring, I've updated the schematic
and PCB files accordingly.

THIS ALSO MARKS THE BEGINNING OF DEVELOPMENT OF THE NEXT BOARD REVISION.

Tested to probably not blow anything up if assembled properly!