Rollup merge of #25702 - killercup:rustdoc/search-primitives, r=Gankro

This minimally changes rustdoc's search as described in #25167.

Additionally, I also cleaned up some parts of the JS code.

There is one more change I made: After each result for a primitive type, I added "(Overview of primitive type)". This further differentiates the result from the module (previously, the only difference was that the module's link was blue). I'm not this is the way to go (this seems to be the only place where we do this) and it's no problem for me to remove that commit.

![std__str_-_rust](https://cloud.githubusercontent.com/assets/20063/7770589/67e8cb26-0090-11e5-8f99-c2a3af9fa37f.png)

cc @steveklabnik (it concerns docs) and @alexcrichton (who made changes to rustdoc previously)