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.

2000/primenum/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [2000 primenum bugs](../../bugs.html#2000_prim
 
 ## To use:
 
-```sh
+```<!---sh-->
     echo n | ./primenum n
 ```
 
@@ -27,7 +27,7 @@ NOTE: `n` is an integer.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -64,7 +64,7 @@ Instead, the program reads input from `stdin` and returns garbled text on
 `stdout`.  Fortunately, you can recover the original message simply by
 running the program a second time.  Try:
 
-```sh
+```<!---sh-->
     ./primenum n < textfile | ./primenum n > textfile2
     diff textfile textfile2
 ```

2000/primenum/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></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    make</code></pre>
 <h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
 <p>The current status of this entry is:</p>
 <pre><code>    STATUS: INABIAF - please **DO NOT** fix</code></pre>
 <p>For more detailed information see <a href="../../bugs.html#2000_primenum">2000 primenum bugs</a>.</p>
 <h2 id="to-use">To use:</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="bu">echo</span> n <span class="kw">|</span> <span class="ex">./primenum</span> n</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    echo n | ./primenum n</code></pre>
 <p>NOTE: <code>n</code> is an integer.</p>
 <h2 id="try">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="ex">./try.sh</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./try.sh</code></pre>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>Don’t read the author remarks until you’re ready for the spoiler.
 Just stop and read the program; it won’t take long. Once you’ve figured
@@ -174,8 +174,8 @@ syntax “mistakes” (e.g. <code>LessThanOrEqualTo</code>) and blatant “erro
 Instead, the program reads input from <code>stdin</code> and returns garbled text on
 <code>stdout</code>. Fortunately, you can recover the original message simply by
 running the program a second time. Try:</p>
-<div class="sourceCode" id="cb5"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./primenum</span> n <span class="op">&lt;</span> textfile <span class="kw">|</span> <span class="ex">./primenum</span> n <span class="op">&gt;</span> textfile2</span>
-<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a>    <span class="fu">diff</span> textfile textfile2</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./primenum n &lt; textfile | ./primenum n &gt; textfile2
+    diff textfile textfile2</code></pre>
 <p>where n is the same number (modulo 64). So, the prime number generator
 is actually a simple text encoder/decoder! Of course, don’t forget that
 argument, otherwise the “bugs” in the program will cause it to crash!</p>