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.

2018/algmyr/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -22,7 +22,7 @@ For more detailed information see [2018 algmyr bugs](../../bugs.html#2018_algmyr
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./prog < prog.c			# Print garbage: might mess up your terminal
     ./prog <file1> <file2> > out.raw
     ./prog -d 2 0 out.raw		# Decode the first (0th) channel out of two
@@ -31,7 +31,7 @@ For more detailed information see [2018 algmyr bugs](../../bugs.html#2018_algmyr
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -164,13 +164,13 @@ standards compliant). This is used to print the usage instructions.
 
 Compiling using
 
-```sh
+```<!---sh-->
     gcc -Wall -Wextra -pedantic
 ```
 
 gives only `-Wmisleading-indentation` which is sensible considering the source code. While
 
-```sh
+```<!---sh-->
     clang -Wall -Wextra -pedantic
 ```
 
@@ -179,7 +179,7 @@ bodies), `-Wstring-plus-int` (since apparently some people think string+`int` is
 concatenation) and one of the weirder warnings I have seen from me splitting a
 negative constant with whitespace. Compiling using
 
-```sh
+```<!---sh-->
     clang -Wall -Wextra -pedantic -Weverything
 ```