Function fetch_rustdoc_json 

pub async fn fetch_rustdoc_json(
    name: &str,
    version: &str,
    client: &ClientWithMiddleware,
    cache: &DiskCache,
) -> Result<RustdocJson>

Fetch the rustdoc JSON for a crate from docs.rs.

Returns Err(DocsError::DocsNotFound) if docs.rs has no successful build.