bug#13207: lisp-mnt.el improvements

[Jonas Bernoulli]

Hello

I extract information from the library headers of all packages mirrored
on the Emacsmirror.  Since many packages don't follow the header
conventions lisp-mnt.el in it's current form isn't always suitable.  So
I have written elx.el which can handle some departure from the standard;
it also includes some additions.

Now I would like to merge some of the changes back into lisp-mnt.el:

1. Add function lm-homepage
   (lm-header "\\(?:x-\\)?\\(?:homepage\\|url\\)")
   These keywords are used quite often, most often without the X- prefix.

2. lm-section-end: the end is now always before the following
   non-comment text

   Many people don't add ;;; Code: after the header.  As a result
   lm-commentary was often way of (like eof!) and lm-commentary returned
   text that isn't part of the commentary but code.

3. lm-header, lm-header-multiline: wrap with save-match-data

4. lm-header-multiline: continuation lines now need to be intended more
   than the first line.  E.g:

   ;; Keyword: value
   ;;  more value

   This is necessary because some built-in libraries contain things
   like:

   ;; Author: Kenichi HANDA <handa@etl.go.jp>
   ;; (according to ack.texi)

   And some third-party libraries contain things like:

   ;; Keywords: key words
   ;; This file is not part of Emacs

   Among the 3500 packages mirrored on the Emacsmirror there are only
   three where this change results in lines intended as continuation
   lines not to be recognised anymore.  At the same time this change
   fixes ~50 errors.

   There now have to be at least two spaces or one tab after the initial
   semicolons for a line to be considered a continuation line.

(1) and (4) should be documented in the info page.  Let me know if you
want to do that.

elx.el contains some more things that could be merged into lisp-mnt.el,
but I would first like to know how these changes are received.

  Jonas

lisp-mnt.patch
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