minor tidy and doc of Json, PaletteGetterWeb mods
Do web requests and file loads concurrently.

This allows a smoother animation.

The web request threads finish by putting their 
parsed responses onto a Chan, which the main
update loop checks and integrates into 
the game state as necessary.

The loading of palettes from file is done 
in this way, too.
tidy only
start in two tone mode
Add option of fullscreen mode (and use it)
Use STM's TChan, not Chan

because isEmptyChan is deprecated.