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.

2000/rince/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [2000 rince bugs](../../bugs.html#2000_rince).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./rince number number2
 ```
 
@@ -28,7 +28,7 @@ different.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -51,7 +51,7 @@ observation.
 
 The simplest way to run it is with no arguments. Just type:
 
-```sh
+```<!---sh-->
     ./rince
 ```
 
@@ -65,7 +65,7 @@ has a built in time machine. Indeed the program knows the speed of light,
 which is used to ensure that we see the "live" pictures. Simply specify
 the fraction of a day to skip forward for each screen refresh. I suggest:
 
-```sh
+```<!---sh-->
     ./rince 0.01
 ```
 
@@ -73,7 +73,7 @@ To display the output (still guessing?) for a given date, specify two
 arguments. The first argument is as before and the second argument is a
 Julian day number (given as a fractional component). E.g.:
 
-```sh
+```<!---sh-->
     ./rince 0 2441193.6
     ./rince 0.01 2441193.6
 ```
@@ -170,7 +170,7 @@ states the following:
 
 Thus we can plot Galileo's discoveries using the following three plots:
 
-```sh
+```<!---sh-->
     ./rince 0 $(./dmy2jd  7.8 1 1610)
     ./rince 0 $(./dmy2jd  8.8 1 1610)
     ./rince 0 $(./dmy2jd 10.8 1 1610)
@@ -180,7 +180,7 @@ However we can go one better by seeing what Galileo would have seen if it
 wasn't cloudy on the 9th. Try:
 
 
-```sh
+```<!---sh-->
     ./rince 0 $(./dmy2jd 9.85 1 1610)
 ```