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.

1993/schnitzi/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [1993 schnitzi bugs](../../bugs.html#1993_schn
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./schnitzi file
 ```
 
@@ -33,14 +33,14 @@ in [1993 schnitzi bugs](../../bugs.html#1993_schnitzi).
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./schnitzi schnitzi.info
     # ask some questions suggested by the author, noted below
 ```
 
 We also suggest you ask the program the following questions:
 
-```sh
+```<!---sh-->
     Who is Mark Schnitzus?
 
     Who was Jack the Ripper ?
@@ -51,7 +51,7 @@ intentional spelling error there.
 
 Try feeding the program source to the program and ask both:
 
-```sh
+```<!---sh-->
     What is cat ?
     What is cat?
 ```