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.

2004/vik2/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./vik2
 ```
 
@@ -127,7 +127,7 @@ speed up the compilation, define the `STOP` symbol to anything from `_3` to
 `_10`. (The default value is `_10` which will make the compilation take some
 time.) Prime numbers up to `2^STOP` will be calculated.
 
-```sh
+```<!---sh-->
     cpp '-DSTOP=_5' '-DFNAME="tmp1.c"' prog.c tmp1.c
 ```
 
@@ -135,20 +135,20 @@ Then use `cpp` or any other
 [pre-processor](https://en.wikipedia.org/wiki/C_preprocessor) to do the actual
 work. This will take some time....
 
-```sh
+```<!---sh-->
     cpp tmp1.c > tmp2.c
 ```
 
 Finally compile the pre-processed file
 
-```sh
+```<!---sh-->
     cc -O tmp2.c -o prog
 ```
 
 Then run the program to reveal all prime numbers up to 32 (if you used
 `STOP=_5` as above):
 
-```sh
+```<!---sh-->
     ./vik2
 ```