std::hash<> could have a clearer index entry

[sdutoit]

Given that there are many specializations of std::hash<>, the index should clearly point to [unord.hash] for the general description.

[jwakely]

It's also a bit difficult to find that it's declared in <functional> if you forget that (as I just found out!) Even if you follow one of the many xrefs to [unord.hash] you then have to go back 22 pages to find the <functional> synopsis that contains it. The section name "unord.hash" gives no clue, and searching for "hash" takes a long time because you have to skip past all the specializations, most of which come earlier in Clause 20. I'm not sure what can be done to improve that though, maybe nothing, the standard isn't meant to be a tutorial or quick reference.

[tkoeppe]

@AlisdairM: Could you please check if this is still a problem?

[jensmaurer]

The index entry for the library name "hash" now points to the right place.

In order to address the other concern, I'll add a "synopsis" subsection for and add a cross-reference to it.