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.

1998/schnitzi/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [1998 schnitzi bugs](../../bugs.html#1998_schn
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./schnitzi n > sort.c
     make sort
     ./sort
@@ -32,14 +32,14 @@ where `n` and `x`, `y` and `z` are numbers.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
 What happens if at the command line you don't specify `n` numbers that the
 program expects? For instance try:
 
-```sh
+```<!---sh-->
     ./schnitzi 5 > sort.c
     make sort
 
@@ -99,7 +99,7 @@ a depth of one.
 So what does it do?  Give it an integer `(1 < n < 27)` on the command
 line, such as
 
-```sh
+```<!---sh-->
     ./schnitzi 5
 ```
 
@@ -109,7 +109,7 @@ them, however, using only `if/else` statements, without arrays or
 looping.  To see the resulting program run, redirect the output from
 `schnitzi` into another file, like this
 
-```sh
+```<!---sh-->
     ./schnitzi 4 > sort.c
 ```