Rustdoc: Named hyperlinks broken in summaries

[frewsxcv]

This link:

http://alexcrichton.com/git2-rs/git2/index.html

displays:

A structure to represent a git [refspec][1].

---

This link:

http://alexcrichton.com/git2-rs/git2/struct.Refspec.html

displays:

A structure to represent a git refspec.

[bluss]

Summaries also render **boldface** verbatim.