message: add_package: treat proc-macros as libraries
  Before this commit crates containing only proc-macros weren't
  documented, as docs.rs treated them as binaries. Proc macros are
  supposed to be documented though, and that behavior was a regression of
  the rustwide deployment.
  This commit fixes the regression by treating proc macros as libraries.
diff: @@ -38,7 +38,7 @@ pub(crate) fn add_package_into_database(conn: &Connection,
  let readme = get_readme(metadata_pkg, source_dir).unwrap_or(None);
  let (release_time, yanked, downloads) = try!(get_release_time_yanked_downloads(metadata_pkg));
  let is_library = match metadata_pkg.targets[0].kind.as_slice() {
  - &[ref kind] if kind == "lib" => true,
  + &[ref kind] if kind == "lib" || kind == "proc-macro" => true,
  _ => false,
  };
  let metadata = Metadata::from_source_dir(source_dir)?;
  