fix markdown footnote problem caused by pandoc

Add "<!-- BEFORE: 1st line of markdown file: FILE/PATH -->"
before the markdown content.  This line appears in the
generated HTML.

Add "<!-- AFTER: last line of markdown file: FILE/PATH -->"
after the markdown content.  This line appears in the
generated HTML.

We test a fix relating to problems produced by `pandoc(1)`
when footnotes are added at the end of generated HTML.
This test is made for `2000/bmeyer/index.html`.

Fixed exit 4 in `bin/md2html.sh that should be exit 5.

Changed `bin/md2html.sh` VERSION from to "1.3 2024-04-14"
to "1.4 2024-04-18".

Run `bin/readme2index.sh -v 1 2000/bmeyer` to perform the above.

2020/ferguson2/recode.html

@@ -133,6 +133,7 @@
 <!-- END: this line ends content from: inc/before-content.default.html -->
 <!-- START: this line starts content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->
 
+<!-- BEFORE: 1st line of markdown file: 2020/ferguson2/recode.md -->
 <h1 id="the-recode-configurator-documentation-and-a-fun-way-to-explore-my-2020-ioccc-enigma-simulator">The recode configurator documentation (and a fun way to explore my 2020 IOCCC Enigma simulator)</h1>
 <p>N.B. At the end of this file I have given a fun exercise that can be used to
 explore my <a href="https://www.cryptomuseum.com/crypto/enigma/index.htm">Enigma machine</a>
@@ -611,6 +612,7 @@ the key you wish to select is</p>
         https://creativecommons.org/licenses/by-sa/4.0/
 
 -->
+<!-- AFTER: last line of markdown file: 2020/ferguson2/recode.md -->
 
 <!-- END: this line ends content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->
 <!-- START: this line starts content from: inc/after-content.default.html -->