add experimental rules to build web site

We add to the top level Makefile, some initial rules that
will facilitate the building of HTML content.

The `bin/md2html.sh` tool as been updated to output HTML comments
about the output during HTML phases 20, 21 and 22.

All entry `index.html` files were updated with some additional HTML
comments as a result of the above.  The top level `location.html`,
`years.html` and `authors.html` have had HTML comments added also
a result.

Sorry (tm Canada 🇨🇦) for the mass update of entry `index.html` files.
Hopefully the times when all of them (often) need to be updated
will soon draw to a close.

1991/cdupont/index.html

@@ -110,6 +110,8 @@
     <a name="content"></a>
 
 <!-- END: this line ends content from: inc/before-content.default.html -->
+<!-- START: this line starts content for HTML phase 20 by: bin/output-index-author.sh via bin/md2html.sh -->
+
 <!-- START: this line starts content generated by: bin/output-index-author.sh -->
 
 <h2 id="author"><a name="author"></a>Author:</h2>
@@ -120,6 +122,10 @@ Dupont</a><br> Location: <a href="../../location.html#FR">FR</a>
 </ul>
 
 <!-- END: next line ends content generated by: bin/output-index-author.sh -->
+
+<!-- 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 -->
+
 <h2 id="to-build">To build:</h2>
 <div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="fu">make</span> all</span></code></pre></div>
 <h2 id="to-use">To use:</h2>
@@ -149,6 +155,10 @@ this license:</p>
 <pre><code>Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)</code></pre>
 <p>For more information, see:
 https://creativecommons.org/licenses/by-sa/4.0/</p>
+
+<!-- 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 -->
+
 <!-- START: this line starts content generated by: bin/output-index-inventory.sh -->
 
 <h1 id="inventory-for-1991cdupont"><a name="inventory"></a>Inventory for
@@ -183,6 +193,8 @@ href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/1991/cdupont/READ
 </ul>
 
 <!-- END: next line ends content generated by: bin/output-index-inventory.sh -->
+
+<!-- END: this line ends content for HTML phase 22 by: bin/output-index-inventory.sh via bin/md2html.sh -->
 <!-- START: this line starts content from: inc/after-content.default.html -->
 
 <!-- END: this line ends content from: inc/after-content.default.html -->