Floppy disk buffer changes are not saved or loaded with the state

[JoeOsborn]

Per https://github.com/copy/v86/blob/master/src/floppy.js#L131 it looks like fda_image is not used anywhere in get_state or set_state. That means if you write to a floppy and make a save state, the write is not recorded.

[uniAIDevs]

I've fixed this issue, I'll add a pull request soon.