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.

2004/gavare/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -10,14 +10,14 @@ for more details.
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./gavare > ioccc_ray.ppm
 ```
 
 Open `ioccc_ray.ppm` with a viewer capable of viewing PPM files. Alternatively,
 if you have ImageMagick installed, you can convert it to a jpeg:
 
-```sh
+```<!---sh-->
     convert ioccc_ray.ppm ioccc_ray.jpg
 ```
 
@@ -28,7 +28,7 @@ and then view `ioccc_ray.jpg` in a graphics viewer, editor or web browser.
 
 If you have `xv(1)` you can do:
 
-```sh
+```<!---sh-->
     ./gavare | xv -
 ```
 
@@ -53,19 +53,19 @@ on `stdout` which theoretically should work in Windows.
 
 To build the configurable and unobfuscated versions:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
 To change the default size from 1024x768 try:
 
-```sh
+```<!---sh-->
     make clobber XX=640 YY=480 alt
 ```
 
 You might also wish to change the anti-alias setting:
 
-```sh
+```<!---sh-->
     make clobber AA=2 alt
 ```
 
@@ -78,7 +78,7 @@ This is not possible with the author's version but it is with the alt versions
 As the Windows version will not compile on most viewers' systems we do not build
 it with `make alt`; instead try:
 
-```sh
+```<!---sh-->
     make alt2
 ```