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.

1990/dg/README.md

@@ -44,7 +44,7 @@ If my preprocessor could hack it, I could write this as one single line rather
 than 4, but when I do that I get a complaint "defines nested too deeply".
 
 
-### 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.

1990/dg/index.html

@@ -418,7 +418,7 @@ which we have done for the wider audience.</p>
 <h2 id="authors-remarks">Author’s remarks:</h2>
 <p>If my preprocessor could hack it, I could write this as one single line rather
 than 4, but when I do that I get a complaint “defines nested too deeply”.</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>

1990/pjr/README.md

@@ -55,7 +55,7 @@ By use of pointers to functions returning a struct of pointers
 to functions!
 
 
-### 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.

1990/pjr/index.html

@@ -425,7 +425,7 @@ well.</p>
 it is done?</p>
 <p>By use of pointers to functions returning a struct of pointers
 to functions!</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>