Call for votes: Add !DATA to MPD spec

[Travis Cobbs]

The draft can be found here:
https://www.ldraw.org/data-language-extension.html

I think I'll clean it up and link out to the MPD extension for the MPD meta commands.

Just to be clear here, the intent (and what I called for votes on) is to add !DATA to the existing MPD spec, not create a new spec. Roland proposed (and I agreed) that it made more sense as an extension to MPD than as an independent thing. Since it is fundamentally tied to MPD, having it be separate would be bad.