message: 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.
diff: @@ -460,9 +460,9 @@ pub trait RegistryData {
  /// Despite the name, this doesn't actually download anything. If the
  /// `.crate` is already downloaded, then it returns [`MaybeLock::Ready`].
  /// If it hasn't been downloaded, then it returns [`MaybeLock::Download`]
  - /// which contains the URL to download. The [`crate::core::package::Download`]
  + /// which contains the URL to download. The [`crate::core::package::Downloads`]
  /// system handles the actual download process. After downloading, it
  - /// calls [`finish_download`] to save the downloaded file.
  + /// calls [`Self::finish_download`] to save the downloaded file.
  ///
  /// `checksum` is currently only used by local registries to verify the
  /// file contents (because local registries never actually download
  @@ -474,7 +474,7 @@ pub trait RegistryData {
  /// Finish a download by saving a `.crate` file to disk.
  ///
  - /// After [`crate::core::package::Download`] has finished a download,
  + /// After [`crate::core::package::Downloads`] has finished a download,
  /// it will call this to save the `.crate` file. This is only relevant
  /// for remote registries. This should validate the checksum and save
  /// the given data to the on-disk cache.
  