SDK Docs: Move constants to their own section (<color>,, etc)

Right now, the docs have the various constant lists mixed in with the list of functions, and they're all linked together properly which is great, but it often means that if i can't remember a color name, dither type, image flip, etc, I need to find the appropriate function in the docs.

For example, the list of all of the available dither types are not listed with, but they are for and there's a link that goes there... It might be nice to have them all listed out separately... (then perhaps go a step further with an image of a stepped-gradient showing what it looks like, or a link to an external page with this, like is done for the playdate.easingFunctions.

And maybe this request doesn't make sense for most of these, since (eg) setColor, setBackgroundColor have different subsets of the color list that are used, so listing them out in their own section might be silly...