add notices to those who wish for a greater challenge

We add the following level-3 header to help people identify text
they may wish to skip if they wish for a greater challenge:

```
```

After that notice we add:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.
```

And sometimes follow with:

```
```

Or sometimes follow with:

```
```

Where the alt code impacts a "greater challenge", we add instead:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program without looking at the Alternate code.

If you get stuck, come back and look at the Alternate code.
```

And where a given command impacts a "greater challenge", we add instead:

```
**If you want a greater challenge, don't read any further**:
just try to understand the program without running the command below.

If you get stuck, come back and run the following command:
```

Perform `make www` to perform the above and test under macOS.

1996/huffman/index.html

@@ -412,10 +412,13 @@ Location: <a href="../../location.html#US">US</a> - <em>United States of America
 <h2 id="try">Try:</h2>
 <pre><code>    ./try.sh</code></pre>
 <h2 id="judges-remarks">Judges’ remarks:</h2>
-<p>If you are still confused and want to read a spoiler, check out
+<p>If you are still confused, check out
 the source and it will be clear as mud!</p>
 <p>And for a misleading hint, consider who won! :-)</p>
-<p>And if you really can’t see what is going on, here is an extra spoiler:</p>
+<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 without running the command below.</p>
+<p>If you get stuck, come back and run the following command:</p>
 <pre><code>    ./huffman &lt; huffman.c 2&gt;/dev/null</code></pre>
 <p>This entry was very well received at the IOCCC BOF.</p>
 <h2 id="authors-remarks">Author’s remarks:</h2>