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/jarijyrki/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -9,7 +9,7 @@ You will need X11 header files and libraries installed to build this program.
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./jarijyrki < infile.info > outfile.info
 ```
 
@@ -18,7 +18,7 @@ You will need a system capable of displaying the results of X Window programs.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./jarijyrki < finance.sheet > myedits.info
 ```
 
@@ -88,7 +88,7 @@ supports are:
 
 ##### Starting
 
-```sh
+```<!---sh-->
     ./jarijyrki < finance.sheet > myedits.info
 ```
 
@@ -144,7 +144,7 @@ To start the spreadsheet program with an existing
 spreadsheet, for instance [finance.sheet](finance.sheet), use the following
 command line:
 
-```sh
+```<!---sh-->
     ./jarijyrki < finance.sheet
 ```
 
@@ -156,7 +156,7 @@ supported by the program.
 
 To start the program with an empty sheet, use
 
-```sh
+```<!---sh-->
     ./jarijyrki < /dev/null
 ```
 
@@ -171,7 +171,7 @@ output. Hence, when the spreadsheet window has come up, you've made your
 changes, and you press the ESC key the program finishes. To save the results in
 a file, the following typical command line would be used:
 
-```sh
+```<!---sh-->
     ./jarijyrki < finance.sheet > myedits.info
 ```