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.

1992/vern/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [1992 vern bugs](../../bugs.html#1992_vern).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./vern 3	# <-- default is 2
 ```
 
@@ -42,7 +42,7 @@ suggested above.  :-)
 
 For a real quick game try:
 
-```sh
+```<!---sh-->
     ./vern
 
     65 55
@@ -124,7 +124,7 @@ wouldn't pass the character limit.  A nice side effect is that the
 initial source is gloriously difficult to peruse. In particular, the Makefile
 does:
 
-```sh
+```<!---sh-->
     sed <vern.c 's/{ /(/g;s/} /)/g;s/;       /#define /' | \
 	sed 's/}      /=/g;s/{        /i/g' >vern.tmp.c
 ```