add hack-a-round for language specified markdown code blocks

When language is specified in a markdown code block such as:

````
```c
    printf("Hello, world!\n");
```
````

is used, the resulting HTML as produced by `pandoc(1)` combined
with our revised `ioccc.css` is not intent the code block well.

A temporary "_hack-a-round_" is to turn the "markdown code language
specifier" into an HTML comment.  For example:

````
```<!---c-->
    printf("Hello, world!\n");
```
````

This commits turns off existing markdown code language specifiers
for now, while preserving our ability to restore them in the future
when a better  "_hack-a-round_" to the "markdown code language
specifier" problem is found.

The HTML impact if this "_hack-a-round_" is to produce HTML that
looks like this:

```
<pre class="&lt;!---c--&gt;"><code> .. </code></pre>
```

We might be able to create a complex set of classes for each markdown
code language (there won't be very many) in `ioccc.css`, or we might
find a more general CSS (or maybe `pandoc(1)`?) solution.

For now, this hack-a-round will have to do.

2020/endoh3/index.html

@@ -141,24 +141,24 @@ Location: <a href="../../location.html#JP">JP</a> - <em>Japan</em></li>
 <!-- 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></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    make</code></pre>
 <p>An alternate version of this program exists. See <a href="#alternate-code">Alternate
 code</a> below.</p>
 <h2 id="to-use">To use:</h2>
-<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./prog</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./prog</code></pre>
 <h2 id="try">Try:</h2>
-<div class="sourceCode" id="cb3"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./run_clock</span></span>
-<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a>    <span class="co"># And watch closely for 15-20 seconds</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./run_clock
+    # And watch closely for 15-20 seconds</code></pre>
 <h2 id="alternate-code">Alternate code:</h2>
 <p>An alternate version of this entry, <a href="prog.alt.c">prog.alt.c</a>, is provided. This
 alternate code uses Unicode letters.</p>
 <h3 id="alternate-build">Alternate build:</h3>
-<div class="sourceCode" id="cb4"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a>    <span class="fu">make</span> alt</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    make alt</code></pre>
 <h3 id="alternate-use">Alternate use:</h3>
 <p>Use <code>prog.alt</code> as you would <code>prog</code> above.</p>
 <h3 id="alternate-try">Alternate try:</h3>
-<div class="sourceCode" id="cb5"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./run_clock.alt</span></span>
-<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a>    <span class="co"># And watch closely for 15-20 seconds</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./run_clock.alt
+    # And watch closely for 15-20 seconds</code></pre>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>You may be tempted to use a mirror. Resist the temptation! Try figuring out how
 the clock hands are drawn. Can you change the program to make it draw a
@@ -167,7 +167,7 @@ familiar (non-mirrored) clock face? Can you add the second hand?</p>
 time might depend on what time it is.</p>
 <h2 id="authors-remarks">Author’s remarks:</h2>
 <p>Prepare a mirror!</p>
-<div class="sourceCode" id="cb6"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb6-1"><a href="#cb6-1" aria-hidden="true" tabindex="-1"></a>    <span class="fu">make</span> clock</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    make clock</code></pre>
 <p>Note: You need to recompile it each run.</p>
 <!--