Added a 40 pin bus expansion connector for a Rev 3 board.

Adds all of the Z80 lines minus HALT* and RFSH*.  Has 2 power and 2 ground connections. 

Bought Rev 2 boards but I think I should skip them and order rev 3 with the expansion connector.

This would require that the WAIT* signal be set to open collector with pull-up from the PSoC for accesses to the expansion connector.

Considering making a TMS9918A Graphics with PS/2 keyboard expansion card. Then this could be a stand-alone unit.

The 40-pin connector could be vertical or horizontal.