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.

2000/natori/index.html

@@ -141,14 +141,14 @@ 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 alt version exists for those in the southern hemisphere (or those who want to
 see what it would be in the southern hemisphere). See <a href="#alternate-code">alternate
 version</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">./natori</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./natori</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">./try.sh</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./try.sh</code></pre>
 <p>Try running this on different days, say a few days apart (even better if the
 Moon phase changes), and each time run it several times in a row (or several
 times in a day).</p>
@@ -160,9 +160,9 @@ input or else just by the code itself. Bonus points if you can make it show all.
 <code>acos(l/2)</code> into <code>acos(-l/2)</code> which we have done in the alternate version.</p>
 <h3 id="alternate-build">Alternate build:</h3>
 <p>To run the alternate code that supports the southern hemisphere:</p>
-<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>
-<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">./natori.alt</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./natori.alt</code></pre>
 <p>Try running this on different days, say a few days apart, and each time run it
 several times in a row (or several times in a day).</p>
 <p>What happens if you run it in the northern hemisphere? Are there any
@@ -170,7 +170,7 @@ differences?</p>
 <p>Can you identify any Moon phases that result in the same output of both
 versions? Or are there any?</p>
 <h3 id="alternate-try">Alternate try:</h3>
-<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="ex">./try.alt.sh</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./try.alt.sh</code></pre>
 <p>Like with <a href="try.sh">try.sh</a>, try using this multiple times in a row or throughout
 the day on different days (if different phases of the Moon you’ll see more of a
 difference, of course).</p>