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/sds/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -18,14 +18,14 @@ For more detailed information see [2004 sds bugs](../../bugs.html#2004_sds).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./sds
 ```
 
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -63,13 +63,13 @@ decoder.
 
 Try it out.  Compile the program, then type
 
-```sh
+```<!---sh-->
     ./sds < sds.c
 ```
 
 You should see the encoder program displayed.  Now save it, like:
 
-```sh
+```<!---sh-->
     ./sds < sds.c > encoder.c
 ```
 
@@ -82,14 +82,14 @@ standard input, and will output the results on the standard output.
 
 You can use it like this (assuming you have a file called remarks):
 
-```sh
+```<!---sh-->
     echo 'Hello, World!' > message
     ./encoder message < remarks > remarks_msg
 ```
 
 Then to decode:
 
-```sh
+```<!---sh-->
     ./sds < remarks_msg
     Hello, World!
 ```