Support for read and write.

Will allow storage of serialized state for each "device".

This change created multiple traits for state info loading.

Fixed it by clearing the screen state of the PPU.

Allows options to go down one level.
Enables custom agent versioning.

By setting proper sound raw values.

Also added all major APU constant addresses.
Disabled serial transfer on state loading.

The DMA transfer was being incorrectly triggered while loading the state.