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.

1991/rince/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -11,7 +11,7 @@ that's fewer than the original program.
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./rince
 ```
 
@@ -30,7 +30,7 @@ The author set the maximum number of moves to 484.
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -41,7 +41,7 @@ configurable maximum number of moves allowed, defaulting to the entry's max,
 
 To reconfigure the maximum number of moves to 700:
 
-```sh
+```<!---sh-->
     make clobber MAXMOVES=700 alt
 ```
 
@@ -50,13 +50,13 @@ To reconfigure the maximum number of moves to 700:
 
 To run the first alt version:
 
-```sh
+```<!---sh-->
     ./rince.alt
 ```
 
 To run the second alt version:
 
-```sh
+```<!---sh-->
     ./rince.alt2
 ```