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.

2014/birken/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```sh
+```<!---sh-->
     make
 ```
 
@@ -11,7 +11,7 @@ there is a firewall issue, and also lets you redefine the timing constant,
 
 ## To use:
 
-```sh
+```<!---sh-->
     ./prog < some_secret_or_something
 
     ./prog http://host[:port]
@@ -20,19 +20,19 @@ there is a firewall issue, and also lets you redefine the timing constant,
 
 ## Try:
 
-```sh
+```<!---sh-->
     ./prog < README.md
 ```
 
 or maybe:
 
-```sh
+```<!---sh-->
     echo "IOCCC 2014!" | ./prog
 ```
 
 Next, try in another terminal, as the above one is running:
 
-```sh
+```<!---sh-->
     ./prog http://127.0.0.1:1701
 ```
 
@@ -55,13 +55,13 @@ described by the author. See [configuration](#configuration) below.
 
 To specify the port to say, 31337, try:
 
-```sh
+```<!---sh-->
     make clobber PORT=31337 alt
 ```
 
 To change the timing constant, `STARDATE`, try:
 
-```sh
+```<!---sh-->
     make clobber TIME=5000000 alt
 ```
 
@@ -101,26 +101,26 @@ the server.
 
 ## To use web server
 
-```sh
+```<!---sh-->
     ./prog < secret_file_to_be_downloaded
 ```
 
 Try using the program's source code as the secret file:
 
-```sh
+```<!---sh-->
     ./prog < prog.c
 ```
 
 ## To use client-side downloader
 
-```sh
+```<!---sh-->
     ./prog http://host[:port]
 ```
 
 The optional port defaults to 1701.  If the web server instance is started on
 the same box, try:
 
-```sh
+```<!---sh-->
     ./prog http://127.0.0.1:1701
 ```
 
@@ -246,7 +246,7 @@ numerical values.
 For space considerations, the following include statements were dropped
 resulting in compiler warnings:
 
-```c
+```<!---c-->
     #include <asm/byteorder.h>
     #include <ctype.h>
     #include <netinet/in.h>