Be more clear about what starting at -04 means.

Deprecation of CRS is done. We're not deprecating or removing
other features. We're not adding new features.

@adoyle Mention of shortcomings is gone. We've resolved the ones I was alluding to (CRS) in getting to draft-butler-geojson-04.

I think I like this one better than #49. Let's close that PR if we have consensus.