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.

2013/cable1/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./cable1 name group1 group2
 ```
 
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -26,39 +26,39 @@ We need not limit ourselves to the two major political parties in the US today.
 
 Let us consider:
 
-```sh
+```<!---sh-->
     ./cable1 Cooper Mac PC
 ```
 
 Simon works for Apple, so you would expect Mac.  :-)
 Landon is a long time Mac user:
 
-```sh
+```<!---sh-->
     ./cable1 Noll Mac PC
 ```
 
 That works too!  Now Leo brings PCs to the IOCCC judging for cross-platform
 testing:
 
-```sh
+```<!---sh-->
     ./cable1 Broukhis Mac PC
 ```
 
 We can test other people.  The late Steve Jobs:
 
-```sh
+```<!---sh-->
     ./cable1 Jobs Mac PC
 ```
 
 That works!  How about Bill?
 
-```sh
+```<!---sh-->
     ./cable1 Gates Mac PC
 ```
 
 A PC guy as expected.  What about that other Steve?
 
-```sh
+```<!---sh-->
     ./cable1 Ballmer Mac PC
 ```