split VersionDeleted from crate-deletes

[syphar]

This is a draft, related to:

• https://rust-lang.zulipchat.com/#narrow/stream/356853-t-docs-rs/topic/glium.20gone
• don't delete full crates from docs.rs when only a version was deleted rust-lang/docs.rs#2163

[syphar]

@Byron what do you think about this?

Alternatively, we could also adapt the documentation, though I believe that crates-index-diff is in a better position to differentiate between crate- and version-deletes than docs.rs :)

[Byron]

I think this is the change I would have wanted as well! Sorry for having let the Deleted variant slide into strange behaviour there, it's clearly misleading the way it's implemented :/.

Let me see that I can get this PR ready for being merged and create a new release.

[Byron]

And here is the new release.