Fixed (ironically) an error when generating error messages for overlapping instructions.
Adding an alias from ret to pop16.pc, and adding support for aliases to mcgen.
Making push16.pc push pc+1 so that ret can return to the right place. The name is weird now, but oh well. Had to bump pop16.pc and sub8.ab down one location to make room for the extra step.
Reworked push16.pc again so it does what you'd expect (push literal PC to the stack), finished call and return and associated tests, all working. Finally! Also expanded the immediate ALU bits from 1 to 2 in the control store, since we need >1 for call.