bug#24283: 25.1; Suggestion: Add to Emacs manual an autogenerated appendix listing packages included with Emacs

[Eli Zaretskii]

> From: nljlistbox2@gmail.com (N. Jackson)
> Date: Sun, 21 Aug 2016 17:31:06 -0300
> 
> If the Emacs manual had an appendix (which could probably be
> automatically generated) that listed all the components that come with
> Emacs but are separate, along with a pointer to their documentation, it
> would, I think be very helpful.
> 
> Then the result of the recipe above could be something like:
> 
>   Found `Calc' in Concept Index.  (Only match)
> 
> And the text in the entry might say something like this:
> 
>   "Calc" is the GNU Emacs advanced desk calculator. Enter `M-: (info 
> "(calc)")' to see the Calc manual.

Patches welcome, but please make sure that appendix doesn't get
typeset in the printed version of the manual, like a few of the other
appendices we have.

Thanks.