Generated docs should list at the top, and link to, methods inside traits and impls

[lkuper]

As noted on rust-dev, right now it's painful to link to the HTML docs for a specific method inside a trait or impl because one has to view source to get an anchor link to the right place. (The anchor links are, in fact, already being generated, just not used.)

[huonw]

Triage visit; I guess it's a WONTFIX for the old rustdoc, and is (hopefully) handled by rustdoc_ng (cc @cmr, @Seldaek).

[emberian]

#8125

[emberian]

cc @Seldaek: this is actually really important.

[Seldaek]

When I add anchors I'll make sure there is a "copy link here thingy" near the anchors themselves so you can easily copy the link to send someone directly somewhere.

[alexcrichton]

This is done with rustdoc_ng, now in-tree and generating docs.