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.

1986/marshall/compilers.html

@@ -162,7 +162,7 @@ because of the call to <code>_exit()</code> (see below).</p>
 enable the optimiser clang will generate code that prints the string twice and
 dumps core just like before! What about the call to <code>_exit()</code>?</p>
 <p>The call was:</p>
-<div class="sourceCode" id="cb1"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb1-1"><a href="#cb1-1" aria-hidden="true" tabindex="-1"></a>    _exit<span class="op">(</span>argv<span class="op">[(</span><span class="dt">int</span><span class="op">)*</span>argc<span class="op">-</span><span class="dv">2</span><span class="op">/</span>cc<span class="op">[</span><span class="dv">1</span><span class="op">*(</span><span class="dt">int</span><span class="op">)*</span>argc<span class="op">]|-</span><span class="dv">1</span><span class="op">&lt;&lt;</span><span class="dv">4</span><span class="op">]);</span></span></code></pre></div>
+<pre class="&lt;!---c--&gt;"><code>    _exit(argv[(int)*argc-2/cc[1*(int)*argc]|-1&lt;&lt;4]);</code></pre>
 <p>Changing it to not refer to these variables and just exit 1 and the problems
 disappear!</p>
 <h3 id="macos">macOS</h3>
@@ -172,9 +172,9 @@ it works fine but if it’s disabled it prints out the string and then enters an
 infinite loop!</p>
 <p>After we fix the infinite loop if we change the <code>_exit()</code> call in macOS and
 disable the optimiser we might get something like:</p>
-<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">$</span> ./marshall</span>
-<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a>          <span class="ex">choo</span> choo</span>
-<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a>    <span class="ex">Segmentation</span> fault: 11</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    $ ./marshall
+          choo choo
+    Segmentation fault: 11</code></pre>
 <p>Observe how it doesn’t print it twice. But of course it segfaults so it’s not
 right either.</p>
 <p>If the optimiser is enabled, however, we will see that it works fine before the