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.

1991/davidguy/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./davidguy ip_address:server.screen
 ```
 
@@ -16,7 +16,7 @@ where `ip_address` in an IP address of an X server.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./davidguy 127.0.0.1:0.0
 ```
 
@@ -24,7 +24,7 @@ Of course, you may need to supply a more reasonable address.  :-)
 
 ## Also try:
 
-```sh
+```<!---sh-->
     cp -f davidguy guydavid
     ./guydavid 127.0.0.1:0.0
 ```

1991/davidguy/index.html

@@ -141,16 +141,16 @@ 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>
 <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">./davidguy</span> ip_address:server.screen</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./davidguy ip_address:server.screen</code></pre>
 <p>where <code>ip_address</code> in an IP address of an X server.</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">./davidguy</span> 127.0.0.1:0.0</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./davidguy 127.0.0.1:0.0</code></pre>
 <p>Of course, you may need to supply a more reasonable address. :-)</p>
 <h2 id="also-try">Also try:</h2>
-<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="fu">cp</span> <span class="at">-f</span> davidguy guydavid</span>
-<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./guydavid</span> 127.0.0.1:0.0</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    cp -f davidguy guydavid
+    ./guydavid 127.0.0.1:0.0</code></pre>
 <p>Can you determine why this makes a difference?</p>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>We permitted this type of entry to win because:</p>