Broken links in docs due to reexports

[martin-t]

Example:

legion::EntityStore vs legion::world::EntityStory - the link to SubWorld on the first one is broken but works on the second one.

Note that there are probably more cases (e.g. link to SoA on the main page) but it seems cargo-deadlinks doesn't always find them all, the output changes on each run. I reported it as deadlinks/cargo-deadlinks#56.

I don't know how to fix this until rust-lang/rust#43466 is merged.