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.

1994/schnitzi/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -23,14 +23,14 @@ For more detailed information see [1994 schnitzi bugs](../../bugs.html#1994_schn
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./schnitzi < textfile
 ```
 
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -49,7 +49,7 @@ buffer size. This is due to a comment which is explained in more detail in
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -62,7 +62,7 @@ feeding the source code to it will not work right.
 
 ### Alternate try:
 
-```sh
+```<!---sh-->
     ./try.alt.sh
 ```
 
@@ -71,7 +71,7 @@ feeding the source code to it will not work right.
 
 Try:
 
-```sh
+```<!---sh-->
     ./schnitzi < schnitzi.c
 ```
 
@@ -96,14 +96,14 @@ is run by redirecting a file into the executable on the command
 line; for instance, for the file 'info', the program
 would be run as follows:
 
-```sh
+```<!---sh-->
     ./schnitzi < info
 ```
 
 The program generates interesting results when its source file is
 used as input:
 
-```sh
+```<!---sh-->
     ./schnitzi < schnitzi.c
 ```