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.

2006/monge/README.md

@@ -248,7 +248,7 @@ changing the definitions of `W`, `H` and `I` at the beginning of the code.
   parameter.
 
 
-### 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.

2006/monge/index.html

@@ -553,7 +553,7 @@ numbers.</li>
 <li>There should be some way to switch from Mandelbrot to Julia with chosen
 parameter.</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>

2006/toledo2/README.md

@@ -222,7 +222,7 @@ In Unix the min 0 on `stty` is required but circa 2001
 it was not required.
 
 
-### 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.

2006/toledo2/index.html

@@ -534,7 +534,7 @@ is not what is needed.</p>
 <p>On PC/DOS you need to add <code>ANSI.SYS</code> to <code>CONFIG.SYS</code>.</p>
 <p>In Unix the min 0 on <code>stty</code> is required but circa 2001
 it was not required.</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>