bug#36767: 26.1; request: add more quick keys to the *Help* buffer

[martin rudalics]

> I fixed up your patch so that it works more reliably, but then I
> remembered why I didn't add the link: We don't know at this point
> whether the symbol in question is documented in the manual.  Adding a
> link to something that fails is bad UI.  And we can't check whether the
> symbol exists in the manual when generating the *Help* buffer, because
> it's slow, and the trade-off (making the command slow versus an extra
> link) is not a good one.

It would be nice to have an etags-like tool that produces a table of all
symbols documented in installed manuals.

martin