Resolve doc warnings for RegistryData
Resolve doc warnings for RegistryData

Specify `Self::finish_download` instead of just `finish_download` and
link to `crate::core::package::Downloads` instead of `Download` as
`Downloads` is the public one, does the actual stuff and `Download` only
stores data.

Signed-off-by: Paul Mabileau <a3aedf8c87c1af3dfeae5f57ddf6d5ae82ad981f@hotmail.fr>

nipunn1313/cargo,nipunn1313/cargo,eminence/cargo,eminence/cargo,rust-lang/cargo,nipunn1313/cargo,rust-lang/cargo,eminence/cargo,rust-lang/cargo,rustyhorde/cargo,nipunn1313/cargo,rustyhorde/cargo,rust-lang/cargo,eminence/cargo,rustyhorde/cargo,rustyhorde/cargo