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.

2020/endoh1/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -10,7 +10,7 @@ code](#alternate-code) below.
 
 ## To use:
 
-```sh
+```<!---sh-->
     # IMPORTANT for macOS: run under Terminal.app
 
     ./prog
@@ -19,7 +19,7 @@ code](#alternate-code) below.
 
 ## Try:
 
-```sh
+```<!---sh-->
     # IMPORTANT for macOS: run under Terminal.app
 
     # Try resizing the terminal window before the first click.
@@ -41,7 +41,7 @@ Author's remarks for more details.
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -94,7 +94,7 @@ All you have to do is (0).  You can test if you are lucky or not.
 
 It uses ncurses:
 
-```sh
+```<!---sh-->
     gcc -o prog prog.c -lncurses
     ./prog
 ```
@@ -200,7 +200,7 @@ Analyze the code.
 
 You can also play with a prepared map.
 
-```sh
+```<!---sh-->
     ./prog ioccc.txt
 ```