Added a callback function to report the state while the VM is running.

The VM state is now output via the callback function defined in the main
function rather than being output directly from the VM functions.
Added command-line options to control state output. Also added verbose flag.
Added a verbose option for load_memory to suppress output unless required.
Added option to output the final accumulator state.
Added a quiet mode.
Merge branch 'feature-state-output' into develop