correctly process non-zero EXIT_CODE, fix 2020/endoh2/README.md

We found cases where pandoc reported a conversion from markdown to
HTML problem that, while reported by the `bin/pandoc-wrapper.sh`
to `bin/md2html.sh`, which in turn reported to error to the tool
calling it, the tool calling `bin/md2html.sh` set `$EXIT_CODE` to
a non-zero value in order to delay the abort but then failed to act
on the non-zero `$EXIT_CODE` value at the end.

In a number of cases when `$EXIT_CODE` was set to non-zero, the
stderr message was labeled as a "Warning" instead of an "ERROR".

Fixed a bug in `bin/gen-authors.sh` that resulted the generation
of invalid markdown/HTML.  An `<hr>` HTML tag inside a `<div>` span
caused pandoc to issue "Div at .. closing implicitly" at the _hr_
HTML tag line.  For some reason, one cannot place a `<hr>`
(horizontal line) inside a `<div ... /div>` span.

Fixed a broken markdown links in `2020/endoh2/README.md` whose error
was hidden by one of the above mentioned problems.

Changed `bin/gen-authors.sh` VERSION from "1.10.1 2024-05-07"
to "1.10.2 2024-05-19" as a result of the above changes.

Changed `bin/gen-location.sh` VERSION from "1.4.1 2024-04-28"
to "1.4.2 2024-05-19" as a result of the above changes.

Changed `bin/gen-top-html.sh` VERSION from "1.4.6 2024-05-05"
to "1.4.5 2024-05-19" as a result of the above changes.

Changed `bin/gen-years.sh` VERSION from "1.3.1 2024-04-28"
to "1.3.2 2024-05-19" as a result of the above changes.

Changed `bin/quick-readme2index.sh` VERSION from "1.1.4 2024-04-13"
to "1.1.5 2024-05-19" as a result of the above changes.

Changed `bin/readme2index.sh` VERSION from "1.2.4 2024-04-14"
to "1.2.5 2024-05-19" as a result of the above changes.

Performed `make www` to test the above under macOS.

2020/endoh2/README.md

@@ -29,11 +29,11 @@ What happens if you do
 
 ## Judges' remarks:
 
-Clever use of the C99 complex data type. The [spoiler](spoiler/spoiler.html) directory
+Clever use of the C99 complex data type. The [spoiler](spoiler/index.html) directory
 contains clues as to how some winning authors create / edit programs into ASCII
 shapes.
 
-With the source from the [spoiler](spoiler/spoiler.html) directory could you make the code
+With the source from the [spoiler](spoiler/index.html) directory could you make the code
 render for a larger terminal window?  How about adding more glyphs?
 
 

2020/endoh2/index.html

@@ -405,10 +405,10 @@ Location: <a href="../../location.html#JP">JP</a> - <em>Japan</em></li>
 <pre><code>    ./prog prog.c</code></pre>
 <p>?</p>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
-<p>Clever use of the C99 complex data type. The <a href="spoiler/spoiler.html">spoiler</a> directory
+<p>Clever use of the C99 complex data type. The <a href="spoiler/index.html">spoiler</a> directory
 contains clues as to how some winning authors create / edit programs into ASCII
 shapes.</p>
-<p>With the source from the <a href="spoiler/spoiler.html">spoiler</a> directory could you make the code
+<p>With the source from the <a href="spoiler/index.html">spoiler</a> directory could you make the code
 render for a larger terminal window? How about adding more glyphs?</p>
 <h2 id="authors-remarks">Author’s remarks:</h2>
 <p>No! Try not. Do, or do not. There is no try.</p>