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.

2019/endoh/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -21,7 +21,7 @@ For more detailed information see [2019 endoh bugs](../../bugs.html#2019_endoh).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./prog
 ```
 
@@ -30,7 +30,7 @@ For more detailed information see [2019 endoh bugs](../../bugs.html#2019_endoh).
 
 If you have `gdb(1)` installed:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -40,7 +40,7 @@ only been tested with linux.
 
 You might also wish to try:
 
-```sh
+```<!---sh-->
     gdb ./prog || lldb ./prog
 ```
 
@@ -59,20 +59,20 @@ ascii` when debugging it to reveal its purpose.
 
 Compile prog.c with no optimization.
 
-```sh
+```<!---sh-->
     cc -g -O0 -o prog prog.c
 ```
 
 Then, run it.  You will see a segmentation fault.
 
-```sh
+```<!---sh-->
     $ ./prog
     Segmentation fault (core dumped)
 ```
 
 Let's debug.  As usual, run it under gdb.
 
-```sh
+```<!---sh-->
     $ gdb ./prog
     (gdb) run
     Starting program: /home/.../prog
@@ -132,7 +132,7 @@ The original program can be used as a GDB command file.
 
 By using this, you can confirm that it is actually a quine.
 
-```sh
+```<!---sh-->
     gdb -q -x prog.c ./prog | sed -n -r 's/#.*:([0-9]+)/\1/p' | awk '{printf "%c",$1}' > prog2.c
     diff prog.c prog2.c
 ```