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.

2013/index.html

@@ -155,10 +155,10 @@ authors submitted very different styles of entries.</p>
 had to print a value 2053 or less when the <code>-i</code> flag was used.</p>
 <p>Several people discovered an undocumented feature in that
 certain comments such as:</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>        <span class="co">///*</span></span></code></pre></div>
+<pre class="&lt;!---c--&gt;"><code>        ///*</code></pre>
 <p>or:</p>
-<div class="sourceCode" id="cb2"><pre class="sourceCode c"><code class="sourceCode c"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a>        <span class="op">*</span>\</span>
-<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a>        <span class="op">/</span></span></code></pre></div>
+<pre class="&lt;!---c--&gt;"><code>        *\
+        /</code></pre>
 <p>were not correctly parsed by the tool. The guidelines stated:</p>
 <pre><code>    In cases where the above summary and the algorithm implemented by
     the IOCCC size tool source code conflict, the algorithm implemented