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.

2020/ferguson1/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [2020 ferguson1 bugs](../../bugs.html#2020_fer
 
 ## To use:
 
-```sh
+```<!---sh-->
     WAIT=N WALLS=[01] EVADE=N SIZE=N MAXSIZE=N GROW=N SHEDS=N SHED=N CANNIBAL=[01] ./prog
     # start pressing some arrow keys
 ```
@@ -87,7 +87,7 @@ and non-zero).
 
 ## Try:
 
-```sh
+```<!---sh-->
     make test
 
     WAIT=75 WALLS=1 CANNIBAL=1 ./prog
@@ -211,7 +211,7 @@ features.
 Because all IOCCC entries should have a man page I have included one (even
 though much of it is what's also above). To render try:
 
-```sh
+```<!---sh-->
     man ./snake.1
 ```