Include `homepage` field in `cargo metadata`

[jyn514]

Describe the problem you are trying to solve

docs.rs wants access to the homepage field in Cargo.toml so it can show it in the sidebar (e.g. https://docs.rs/crate/tokio/0.3.4 links to https://tokio.rs/).

Describe the solution you'd like

cargo metadata should include a homepage field for every package, the same way it has a repository field for each.

Notes

I'm a little confused why this is working currently in docs.rs - we use custom serialization instead of https://docs.rs/cargo_metadata, but I don't see how we could deserialize data that wasn't there in the first place. But I ran database query and there are definitely a lot of projects with homepages. Maybe this changed semi-recently?

[jyn514]

The documentation field would also be useful.

[jyn514]

It turns out this is present in 1.49 and I was testing with 1.48. Sorry for the noise!