Use ctrl_0d for carriage return in ctrl_0c
Decouple ctrl_08 and ctrl_0b
Use the fill directive to make the tab stop buffer area
Remove an unnecssary jump from move-to handler
Rename memory access routines for clarity
Decouple do_mem_jsr from process_byte
Refactor process_byte so its subroutines return to it with RTS
Remove an unused instruction
Clarify operation of line feed