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.

2006/sloane/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -11,7 +11,7 @@ code](#original-code) below.
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./slone.alt
 ```
 
@@ -24,7 +24,7 @@ problematic for some people, can be configured to different speeds by way of the
 value used in `usleep()`. The default is `75000` but you can easily change
 it. To do so try:
 
-```sh
+```<!---sh-->
     make clobber SLEEP=70000 clobber alt
     ./sloane.alt
 ```
@@ -32,7 +32,7 @@ it. To do so try:
 If you wish to make it like the original, as if the below [Original
 code](#original-code) was being used, you can do:
 
-```sh
+```<!---sh-->
     make SLEEP=0 clobber alt
     ./sloane.alt
 ```
@@ -46,14 +46,14 @@ Should you wish to see the original you may do so with the original code,
 
 ### Original build:
 
-```sh
+```<!---sh-->
     make clobber all
 ```
 
 
 ### Original use:
 
-```sh
+```<!---sh-->
     ./sloane
 ```