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/vanb/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [1993 vanb bugs](../../bugs.html#1993_vanb).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./vanb 'exp'
 ```
 
@@ -28,7 +28,7 @@ hexadecimal and decimal numbers.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -133,7 +133,7 @@ Here's a version of the program before it got formatted into the VIII,
 augmented with comments showing where each state begins. `N1` and `N2` are
 notes:
 
-```c
+```<!---c-->
     #define O5 main
     O5(O2,O7,O3)char**O7;
     {
@@ -180,14 +180,14 @@ printf, and sends the parser to state `012` (which is `<E>`).
 
 The `E` and `T` states work like this:
 
-```c
+```<!---c-->
     int e(){ return eprime( t() ); }
 ```
 
 
 The `E'` and `T'` states work like this:
 
-```c
+```<!---c-->
     int eprime( int intermediate )
     {
 	if( ch == '+' )
@@ -202,7 +202,7 @@ The `E'` and `T'` states work like this:
 The `D`, `X` and `O` states work like this (they assume that they're initially
 called with `0`):
 
-```c
+```<!---c-->
     int octal( int intermediate )
     {
 	if( ch>='0' && ch<='7' )