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.

1996/schweikh3/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -12,7 +12,7 @@ It may render your system unusable for a limited amount of time
 or force you to reboot using the Big Red Button!  This is **NOT** a joke.
 You have been warned.
 
-```sh
+```<!---sh-->
     ./schweikh3
 ```
 
@@ -27,7 +27,7 @@ systems.
 
 But still it is a useful utility.  To use try:
 
-```sh
+```<!---sh-->
     ./schweikh3
 ```
 
@@ -57,7 +57,7 @@ You have to select maximum ANSI C conformance of your
 compiler. The source fails to compile under a C++ compiler due to
 the `new' identifier which is a C++ reserved word:
 
-```sh
+```<!---sh-->
     $ g++ schweikh3.c
     schweikh3.c:9: parse error before `new'
     schweikh3.c:16: parse error before `new'
@@ -71,7 +71,7 @@ the `new' identifier which is a C++ reserved word:
 The source fails to compile on compilers that recognize the inline
 keyword by default, e.g. gcc:
 
-```sh
+```<!---sh-->
     $ gcc schweikh3.c
     schweikh3.c:46: parse error before `void'
     schweikh3.c: In function `main':