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.

1986/marshall/compilers.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: 1986/marshall/compilers.md -->
 <h1 id="conflicting-compilers-and-optimisers-that-broke-this-entry-in-2023">Conflicting compilers and optimisers that broke this entry in 2023</h1>
 <p>As briefly noted in the <a href="README.md">README.md</a> gcc and clang caused different
 problems with this entry depending on the optimiser being enabled or not, where
@@ -208,6 +209,7 @@ eventually could?</p>
         https://creativecommons.org/licenses/by-sa/4.0/
 
 -->
+<!-- AFTER: last line of markdown file: 1986/marshall/compilers.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 -->

1986/marshall/index.html

@@ -151,6 +151,7 @@ Location: <a href="../../location.html#US">US</a> - <em>United States of America
 <!-- END: this line ends content for HTML phase 20 by: bin/output-index-author.sh via bin/md2html.sh -->
 <!-- START: this line starts content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->
 
+<!-- BEFORE: 1st line of markdown file: 1986/marshall/README.md -->
 <h2 id="to-build">To build:</h2>
 <pre><code>    make all</code></pre>
 <p>NOTE: we FORCE disable the optimiser due to a funny problem with different
@@ -197,6 +198,7 @@ from printing a program!</p>
         https://creativecommons.org/licenses/by-sa/4.0/
 
 -->
+<!-- AFTER: last line of markdown file: 1986/marshall/README.md -->
 
 <!-- END: this line ends content for HTML phase 21 by: bin/pandoc-wrapper.sh via bin/md2html.sh -->
 <!-- START: this line starts content for HTML phase 22 by: bin/output-index-inventory.sh via bin/md2html.sh -->