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/hou/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make all
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [2013 hou bugs](../../bugs.html#2013_hou).
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./hou [scene-file-name] [options]
 ```
 
@@ -29,7 +29,7 @@ effects should be more or less recognizable when you see 16.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
@@ -62,7 +62,7 @@ This program will loop infinitely while progressively refining a
 NOTE: the author refers to [a.c](a.c), placed in a gzipped file `a.c.gz`. We do not
 include it but it can be generated like:
 
-```sh
+```<!---sh-->
     cc -Wall hou.c -o hou -lm
     ./hou > a.c
 ```
@@ -78,7 +78,7 @@ needing to create a temporary file.
 This program is a programmable rendering engine with a built-in default scene.
 The standard command line is:
 
-```sh
+```<!---sh-->
     ./hou [scene-file-name] [options]
 ```