Started working on pushing PC

Reworked PUSH into push8.imm and push8.? (for future implementation of other non-immediate push8s). Implemented push16.imm and push16.? including their unit test and register transfer diagram. Started working on push16.pc, but ran into an issue where PC is incremented within FETCH, so if we push it as part of push16.pc then we’re actually pushing PC+1. Need to figure out if that’s okay, or if we need to rework where inc_pc is triggered in the fetch process.