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.

1989/ovdluhe/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -11,7 +11,7 @@ To get this to compile with a modern CPP, we had to replace `#D` with `#define`.
 
 Run the program this way:
 
-```sh
+```<!---sh-->
     ./ovdluhe < textfile
 ```
 
@@ -21,7 +21,7 @@ by chance or is killed.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh ; sleep 2 ; ./try.sh
 ```
 
@@ -34,7 +34,7 @@ it's a `#define` it's easy to set up.
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make P=9 clobber alt
 ```
 
@@ -46,14 +46,14 @@ program to fail and a negative value will cause a compilation error.
 
 ### Alternate use:
 
-```sh
+```<!---sh-->
     ./ovdluhe.alt
 ```
 
 
 ### Alternate try:
 
-```sh
+```<!---sh-->
     ./try.alt.sh
 
     P=5 ./try.alt.sh