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/omoikane/README.md

@@ -193,7 +193,7 @@ Note that on MingW, `stdin` and `stdout` are not opened in binary mode by
 default, this means `Nyaruko` may not faithfully encode files on MingW.
 
 
-### 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/omoikane/index.html

@@ -523,7 +523,7 @@ combinations:</p>
 </ul>
 <p>Note that on MingW, <code>stdin</code> and <code>stdout</code> are not opened in binary mode by
 default, this means <code>Nyaruko</code> may not faithfully encode files on MingW.</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>