rustdoc: Descriptions on statics disrupt the layout

[passcod]

Using this sample source file: https://gist.github.com/passcod/748067f10d2aa4ecaa4e

Single-line description on static:

---

Multi-line:

---

That makes documenting statics useless at best when rendering the docs.

[alexcrichton]

The values of statics are no longer rendered, so this is now fixed!