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.

2019/karns/index.html

@@ -141,7 +141,7 @@ 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>
 <p>NOTE: we disable the optimiser because this program has problems with it
 enabled.</p>
 <h3 id="bugs-and-misfeatures">Bugs and (Mis)features:</h3>
@@ -149,14 +149,14 @@ enabled.</p>
 <pre><code>    STATUS: INABIAF - please **DO NOT** fix</code></pre>
 <p>For more detailed information see <a href="../../bugs.html#2019_karns">2019 karns 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="ex">./prog</span> <span class="op">&lt;</span> textfile_that_fits_on_the_screen</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./prog &lt; textfile_that_fits_on_the_screen</code></pre>
 <p>You might want to type:</p>
-<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">reset</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    reset</code></pre>
 <p>after running the program to restore the terminal to its previous state.</p>
 <h2 id="try">Try:</h2>
-<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">./try.sh</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./try.sh</code></pre>
 <p>If you have more time you might want to try:</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="ex">./prog</span> <span class="op">&lt;</span> README.md</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./prog &lt; README.md</code></pre>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
 <p>If you typically get lost in mazes, watching this program run might – or might
 not, YMMV – teach you how to find your way in a maze. The algorithm is
@@ -179,13 +179,13 @@ adjacent nodes that are also spaces. Nodes that aren’t spaces are not
 connected with anything.</p>
 <h3 id="compiling-and-running">Compiling and Running:</h3>
 <p>This program usually compiles under both GCC and clang. Build with:</p>
-<div class="sourceCode" id="cb7"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb7-1"><a href="#cb7-1" aria-hidden="true" tabindex="-1"></a>    <span class="va">$(</span><span class="ex">CC</span><span class="va">)</span> <span class="at">-std</span><span class="op">=</span>c99 <span class="at">-o</span> tbfs prog.c</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    $(CC) -std=c99 -o tbfs prog.c</code></pre>
 <p>where <code>$(CC)</code> is cc, gcc, clang, or some other C compiler.</p>
 <p>You can then run it with:</p>
-<div class="sourceCode" id="cb8"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb8-1"><a href="#cb8-1" aria-hidden="true" tabindex="-1"></a>    <span class="fu">cat</span> <span class="op">&lt;</span>input file<span class="op">&gt;</span> <span class="kw">|</span> <span class="ex">./tbfs</span></span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    cat &lt;input file&gt; | ./tbfs</code></pre>
 <p>Examples:</p>
-<div class="sourceCode" id="cb9"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb9-1"><a href="#cb9-1" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./tbfs</span> <span class="op">&lt;</span> maze</span>
-<span id="cb9-2"><a href="#cb9-2" aria-hidden="true" tabindex="-1"></a>    <span class="ex">./tbfs</span> <span class="op">&lt;</span> prog.c</span></code></pre></div>
+<pre class="&lt;!---sh--&gt;"><code>    ./tbfs &lt; maze
+    ./tbfs &lt; prog.c</code></pre>
 <h3 id="issues">Issues</h3>
 <ul>
 <li>The program must be ran in a terminal that supports ANSI escape codes for