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.

2015/burton/README.md

@@ -1,19 +1,19 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./prog "expression"
 ```
 
 or:
 
-```sh
+```<!---sh-->
     ./prog
 ```
 
@@ -22,13 +22,13 @@ Type in expressions on standard input.
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./try.sh
 ```
 
 Notice how the script reads in from a file. If you type just:
 
-```sh
+```<!---sh-->
     ./prog
 ```
 
@@ -37,7 +37,7 @@ it will prompt you in the same way. Send ctrl-c to exit.
 
 Finally, if you wish to read the man page:
 
-```sh
+```<!---sh-->
     man ./calc.1
 ```
 
@@ -51,7 +51,7 @@ author's remarks below.
 
 ### Alternate build:
 
-```sh
+```<!---sh-->
     make alt
 ```
 
@@ -109,7 +109,7 @@ Yes, this is another calculator program.
 However, unlike any other calculator source code the author is aware of,
 this one contains no digits.  At all.  Anywhere.  As in
 
-```sh
+```<!---sh-->
     grep '[0-9]' prog.c || echo no digits!
 ```
 
@@ -222,7 +222,7 @@ With `-Wall -std=c99`, both are quite noisy, and all can be ignored:
 If the program name begins with an `e`, it echoes `stdin` to `stdout`.
 This allows for a convenient test suite:
 
-```sh
+```<!---sh-->
     ln -sf prog eprog
     PATH=. eprog < test.in | diff - test.out
 ```