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.

1994/tvr/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -22,7 +22,7 @@ For more detailed information see [1994 tvr bugs](../../bugs.html#1994_tvr).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./tvr mode screensize/2 < colormapfile
 ```
 
@@ -31,7 +31,7 @@ Mode may be a value from 0 to 12.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.color.sh			# for colour displays
     ./try.bw.sh			# for Black & White displays
 ```
@@ -44,14 +44,14 @@ The author provided us a spoiler version that might be of interest to some.
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
 
 ### Alternate use:
 
-```sh
+```<!---sh-->
     ./tvr.alt altmode screensize/2 < colormapfile
 ```
 
@@ -61,7 +61,7 @@ where `altmode` `1` - `4` correspond to mode `0` - `3` in the original entry and
 
 ### Alternate try:
 
-```sh
+```<!---sh-->
     ./try.alt.color.sh			# for colour displays
     ./try.alt.bw.sh			# for Black & White displays
 ```
@@ -123,7 +123,7 @@ the fourth is a variation of that with more nice effects.
 
 ### Usage:
 
-```sh
+```<!---sh-->
     ./tvr mode screensize/2 < colormapfile
 ```