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.

2012/deckmyn/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -18,14 +18,14 @@ For more detailed information see [2012 deckmyn bugs](../../bugs.html#2012_deckm
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./deckmyn "$(cat deckmyn.c)" "$(cat musicfile.txt)" > sheetmusic.pbm
 ```
 
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -59,13 +59,13 @@ You need the source code and example input (either one of the example files, or
 manual input as below) ready and a program capable of showing [.pbm bitmap
 format](https://en.wikipedia.org/wiki/Netpbm) images.
 
-```sh
+```<!---sh-->
     ./deckmyn "`cat deckmyn.c`" "`cat example_greensleeves`" > greensleeves.pbm
 ```
 
 If you have macOS you can open the image like:
 
-```sh
+```<!---sh-->
     open greensleeves.pbm
 ```
 
@@ -73,13 +73,13 @@ If you have macOS you can open the image like:
 normally open an image.
 
 
-```sh
+```<!---sh-->
     ./deckmyn "`cat deckmyn.c`" "KF m44c4 c4 g4 g4 :  a4 a4 g2 :; " > short_bass.pbm
 ```
 
 If you have macOS you can open the image like:
 
-```sh
+```<!---sh-->
     open short_bass.pbm
 ```