deprecate quick_collection, simplify docs

[michaelkirk]

• [x] I agree to follow the project's code of conduct.

• [x] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

The real motivation for this pull request, is that I was trying to look up some basic usage of the geojson crate and it took me uncomfortably long. Our documentation has grown over time and become a bit long winded in my experience.

So I was looking for ways to simplify our documentation, and noticed the couple paragraphs devoted to quick_collection. Since quick_collection converts &GeoJson -> Result<geo_types::GeometryCollection>, I think it will be more discoverable under the idiomatic TryFrom trait, and because it's working like the idiomatic TryFrom trait, I think we can truncate some of the documentation.

[lnicola]

bors d+

(needs rebase)

[bors[bot]]

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[michaelkirk]

Sorry that I didn't merge this a long time ago!

I've made a couple minor changes but the thrust is the same. Can I get another review?