support single-byte pointers (addresses)

For 65Org32 and for small-memory model of 65Org16, we need a build-time option to support single-byte addresses.

This means changing the state machine for
  zero page indirections
  PC push and pull for subroutines and interrupts (both call and return)
  operand fetch for three-byte instructions

Also changing the address bus logic for zero page and stack addresses

Maybe other changes
