Added magnet pockets and verified cutout for switches is functional.

Cutout in coupler for alignment tabs is not quite right, still reqires filing for the bottom
Updated board to be compatible with milling fabrication (e.g. a CNC mill with
an engraving tool for isolation routing). However, actual isolution routed board
is nonfunctional because the design relies upon through-plated holes to connect
the top and bottom traces.
Added serial output when commands are received for easier debugging of newly
flashed boards.