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.

archive/historic/README.md

@@ -79,7 +79,7 @@ Machine](https://web.archive.org) as of [2022 Dec
 
 *HINT*: To uncompress a given bzip2 compressed tarball file, use:
 
-```sh
+```<!---sh-->
 tar -jxvf file.tar.bz2
 ```
 
@@ -88,7 +88,7 @@ where "_file.tar.bz2_" is the name of a file found in this directory.
 To uncompress all of the 2022 Dec 28 archive using the year based
 bzip2 compressed tarball files:
 
-```sh
+```<!---sh-->
 for year in 198{4,5,6,7,8,9} 199{0,1,2,3,4,5,6,8} 200{0,1,4,5,6} 201{1,2,3,4,5,8,9} 2020; do
     rm -rf "$year"
     tar -jxvf "archive-$year.tar.bz2"