[release-branch.go1.7] godoc: allow nested toggles and toggles with <a name>

Toggles can now be nested within one another. They can also be
referenced using an <a> element with the name attribute, rather than
an element with the "id" attribute.

Updates golang/go#17574.

Change-Id: I43c17499a6879e983a79a74e14c99128296288e1
Reviewed-on: https://go-review.googlesource.com/34825
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-on: https://go-review.googlesource.com/35094
Reviewed-by: Chris Broadfoot <cbro@golang.org>
3 files changed