Add doc attributes to proc_macro crate

This adds the same logo and favicon as the rest of the std docs.

src/libproc_macro/lib.rs

@@ -29,6 +29,13 @@
 #![crate_type = "dylib"]
 #![deny(warnings)]
 #![deny(missing_docs)]
+#![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
+       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       html_playground_url = "https://play.rust-lang.org/",
+       issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
+       test(no_crate_inject, attr(deny(warnings))),
+       test(attr(allow(dead_code, deprecated, unused_variables, unused_mut))))]
 
 #![feature(rustc_private)]
 #![feature(staged_api)]