Reorganizes source/utilities.
SUB_VWATCH()
Since `vwatch_linenumber` is a shared variable, it doesn't need to be passed to `SUB_VWATCH()`.
F9 (or clicking a line number) will toggle a breakpoint; When running a program, F8 will pause/step line by line, F9 will still be usable to toggle breakpoints and F5 will continue execution. ESC exits $DEBUG mode.