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.

README.html

@@ -194,7 +194,7 @@ you encounter should give you more appreciation for the entry.</p>
 <p>If you have the energy to type in the text, or if you have access to a machine
 readable version of these programs, you should next consider some preprocessing
 such as:</p>
-<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">sed</span> <span class="at">-e</span> <span class="st">&#39;/^#.*include/d&#39;</span> prog.c <span class="kw">|</span> <span class="fu">cc</span> <span class="at">-E</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>sed -e &#39;/^#.*include/d&#39; prog.c | cc -E</code></pre>
 <p>This strips away comments and expands the program’s macros without having things
 such as includes and macros cluttering up the output. If the entry requires or
 suggests the use of compile line options (such as <code>-Dindex=strchr</code>) they should