Animate map using shader

[joetsoi]

Use a shader that takes a greyscale image and a 1D colour lookup table to draw the map image, this would probably require something like implementing a new ggez::graphics::Drawable type as ggez only currently allows us to create rgba8 images.

So a new image type which uses gfx::formats to allow single channel textures. This probably could also for the flashing knight images either in the map, select knight or encounter scenes.

[joetsoi]

https://gamedev.stackexchange.com/questions/43294/creating-a-retro-style-palette-swapping-effect-in-opengl/43313#43313

sticking to just using more textures instead of shaders