A couple of changes related to media queries

[chungyc]

These are a couple of changes related to media queries:

• Adds the all media type. A reference mentions that media types other than all, screen, and print were deprecated, so documentation was updated to mention this fact.

• Adds support for the prefers-color-scheme media feature.

I have also added a few documentation comments while making these changes. If they were intentionally omitted for other functions, then I'd be happy to remove them.

[turion]

Thanks a lot! Just a quick question about the haddocks.