Slight change in 'greater challenge' line

In the line in README.md and index.html files that said:

    ### NOTICE to those who wish for a greater challenge

I added a ':' at the end of the line.

There were some entries that had a link fix in the index.html file but I
only looked up through 1995/leo as those still have to have a 'look and
feel' check and it would just slow things down.

2012/kang/README.md

@@ -150,7 +150,7 @@ The design of the program explicitly allows for `EOF` even if it does not equal
 endian-independent.
 
 
-### NOTICE to those who wish for a greater challenge
+### NOTICE to those who wish for a greater challenge:
 
 **If you want a greater challenge, don't read any further**:
 just try to understand the program via the source.

2012/kang/index.html

@@ -493,7 +493,7 @@ character set and two’s complement representation.</li>
 <code>-1</code> (it has to be negative per the standard but not necessarily <code>-1</code>) and both
 <code>signed char</code> and <code>unsigned char</code>, for example. Furthermore it is
 endian-independent.</p>
-<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge</h3>
+<h3 id="notice-to-those-who-wish-for-a-greater-challenge">NOTICE to those who wish for a greater challenge:</h3>
 <p><strong>If you want a greater challenge, don’t read any further</strong>:
 just try to understand the program via the source.</p>
 <p>If you get stuck, come back and read below for additional hints and information.</p>