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.

1991/brnstnd/index.html

@@ -141,11 +141,11 @@ Location: <a href="../../location.html#US">US</a> - <em>United States of America
 <!-- 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>
+<pre class="&lt;!---sh--&gt;"><code>    make all</code></pre>
 <h2 id="try">Try:</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">./try.sh</span></span>
-<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a></span>
-<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./sorta</span> <span class="op">&lt;</span> sorta.itailrec</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./try.sh
+
+    ./sorta &lt; sorta.itailrec</code></pre>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>For info on more examples, read the <a href="sorta.README.html">sorta.README.html</a> web page.</p>
 <p>The author wished to win the “most useful program” award and documented this in