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.

1987/heckbert/index.html

@@ -141,17 +141,17 @@ 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>
 <p>On System V systems, we had to compile with <code>-Dindex=strchr</code>.
 To compile on a 16 bit machine, change 300000 to 30000.</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">./heckbert</span> col <span class="op">&lt;</span> file</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./heckbert col &lt; file</code></pre>
 <p>where col is the number of columns to fold at and file is the file to fold.</p>
 <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>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>Folding at the wrong length may be equivalent to a “Spindle or Mutilate” operation. For example:</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="ex">./heckbert</span> 40 <span class="op">&lt;</span> heckbert.c <span class="op">&gt;</span> ph.c <span class="kw">;</span> <span class="fu">make</span> ph <span class="kw">;</span> <span class="ex">./ph</span> 20 <span class="op">&lt;</span> heckbert.c <span class="op">&gt;</span> bar.c <span class="kw">;</span> <span class="fu">make</span> bar</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./heckbert 40 &lt; heckbert.c &gt; ph.c ; make ph ; ./ph 20 &lt; heckbert.c &gt; bar.c ; make bar</code></pre>
 <p>Try not to
 <a href="https://repository.library.brown.edu/studio/item/bdr:788264/PDF/">Fold, Spindle or Mutilate</a>
 files. :-)</p>