Record the result of 500 rolls in D20 mode.

This was done on the master branch, commit 2b5e63b9.

Signed-off-by: Russell Steicke <russells@adelie.cx>
Add the D1 and D2 modes as Easter eggs.

D1 and D2 modes can only be reached by wrapping around the mode
setting from D100 back to the start, twice without stopping.  On the
second wrap around, D1 and D2 modes will appear.

Signed-off-by: Russell Steicke <russells@adelie.cx>
Add a circuit diagram.

This circuit diagram works for point to point wiring as in the
prototype, but may need revision for the PCB.

Signed-off-by: Russell Steicke <russells@adelie.cx>