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.

2011/fredriksson/README.md

@@ -199,7 +199,7 @@ Just say
   (Btw, tcc has its roots in IOCCC...)
 
 
-### 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.

2011/fredriksson/index.html

@@ -536,7 +536,7 @@ C99, or long lines as an extension. This code has been tested on:</p></li>
 <li><p>AIX 5.3, IBM eServer p5-550, gcc 3.3.3 and AIX CC Version 6</p>
 <p>(Btw, tcc has its roots in IOCCC…)</p></li>
 </ul>
-<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>