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/rince/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -22,7 +22,7 @@ For more detailed information see [bugs report with 1993/rince](../../bugs.html#
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./rince [cabbage]
 ```
 
@@ -37,13 +37,13 @@ Some people may want to slow down the game by increasing the
 value 17 in the lines:
 
 
-```c
+```<!---c-->
     struct timeval v= {0,1<<17} ;
 ```
 
 and
 
-```c
+```<!---c-->
     refresh(),c=select(k,&y,0,0,(v.tv_usec=1<<17,&v))?getch():0;
 ```
 
@@ -57,7 +57,7 @@ changed).
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make SLEEP=18 clobber alt
 ```
 
@@ -107,7 +107,7 @@ with the curses library (typically `/lib/libcurses.a` for static libraries)
 used. It has been suggested that the following gcc command may help:
 
 
-```sh
+```<!---sh-->
     gcc -fno-builtin -I/usr/include -o rince rince.c -lcurses -ltermcap
 ```