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.

1993/cmills/README.md

@@ -4,7 +4,7 @@ We recommend you try the alt version first so you can get a better idea of what
 this entry was like back in 1993. See the [original code](#original-code)
 section below to run the original.
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -16,7 +16,7 @@ requires X11?](../../faq.html#X11macos).
 
 To configure how many microseconds to sleep before updates try:
 
-```sh
+```<!---sh-->
     make clobber SLEEP=200 alt
 ```
 
@@ -34,7 +34,7 @@ For more detailed information see [1993 cmills bugs](../../bugs.html#1993_cmills
 
 ## To use:
 
-```sh
+```<!---sh-->
     DISPLAY="your_X_server_display"
     export DISPLAY
     ./cmills.alt [speed]	# must be run on an X11 server
@@ -56,7 +56,7 @@ on but you can use the original without any delays if you wish.
 
 ### Original build:
 
-```sh
+```<!---sh-->
     make all
 ```