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/ferguson1/cannibalism.log.html

@@ -274,7 +274,7 @@ most of them.</p>
 <h2 id="example-5-snake-moving-left-with-snake-inside-itsself">Example 5: snake moving left with snake inside itsself</h2>
 <p>Another example invocation where the snake head is in the snake and where the snake
 hadn’t yet moved (that is it was still growing):</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="va">CANNIBAL</span><span class="op">=</span>1 <span class="va">SIZE</span><span class="op">=</span>1500 <span class="va">GROW</span><span class="op">=</span>2 <span class="va">MAXSIZE</span><span class="op">=</span>1600 <span class="ex">./prog</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    CANNIBAL=1 SIZE=1500 GROW=2 MAXSIZE=1600 ./prog</code></pre>
 <p>It looked like:</p>
 <pre><code>    X:55/89 Y:11/25 S:1564/1600 B:32
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