Add "power save" toggle to reduce electrical interference

[asiekierka]

It appears that TinyZoo halts the CPU at such a high frequency on GBC (due to all the interrupts going on) that the electrical interference noise actually becomes audible! Allow the users to choose between power saving (and said noise) or no power saving (and reduced noise)

[asiekierka]

This is mostly done, but wait_vbl_done() will still halt even when power save mode is disabled. Only the ones which run while the HBlank handler (for multicolor display on CGB) is in place need to be patched, however.