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.

2018/burton2/discrepancies.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: 2018/burton2/discrepancies.md -->
 <p>The values below are the field-by-field difference <code>iocccsize - ioc</code>.
 (<code>&gt;0</code> means <code>iocccsize</code> counted more than <code>ioc</code>, <code>&lt;0</code> <code>ioc</code> counted more)</p>
 <pre><code>    cl: lines, cw: words, cc: chars, ci: rule2, ts: saved, kw: keywords, ks: kw_saved
@@ -208,6 +209,7 @@ rendering this not a keyword, even in disguise</p>
         https://creativecommons.org/licenses/by-sa/4.0/
 
 -->
+<!-- AFTER: last line of markdown file: 2018/burton2/discrepancies.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 -->