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.

2019/dogon/index.html

@@ -565,17 +565,6 @@ resulting <code>F</code> in hexadecimal…</p>
 <p>And yes, the layout hint involves a mix of the most trendy typographical
 character juxtaposed against a very ancient one, not to mention the program
 includes some famous name dropping and documents itself as usual.</p>
-<h3 id="further-spoilers-engineering-and-obfuscation-galore">Further spoilers, engineering, and obfuscation galore:</h3>
-<p>Those wait for you, curious and intrepid reader, in the attached
-<a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/dogon/apholife.c">apholife.c</a> file, which is a partially obfuscated version of the
-program I wrote with a lot of helpful annotations and comments for myself and
-posterity, revealing some of the magic under the hood. This program is also a
-somewhat improved version which uses <code>ldexp()</code>s in the draw routine and has
-bigger constants, so it can zoom up to level 1024 if memory allows, and it tries
-its best to avoid dumping core on the poor user when its memory runs out, rather
-it enters freeze mode where you can still travel in calculated frozen
-space-time. Well, it’s not nice and tame, it even has an escape key, usage
-message, and to top it all it even avoids <code>gets(3)</code>!</p>
 <h3 id="special-thanks">Special thanks:</h3>
 <p>To Tom Rockiki, the original co-writer of Golly, a personal friend and hashlife
 master, who reviewed some earlier versions of the entry and freely shared some
@@ -589,6 +578,21 @@ most obfuscated way of calculating the GOL function on a 64 bits <code>8*8</code
     (ts1 | s1)) &amp; ((ts0 ^ s0) | a); }</code></pre>
 <p>This uses only 19 bitwise operations and six shifts to calculate the inner 6x6
 next generation bits of the input 8x8 !</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 via the source.</p>
+<p>If you get stuck, come back and read below for additional hints and information.</p>
+<h3 id="further-information-engineering-and-obfuscation-galore">Further information, engineering, and obfuscation galore:</h3>
+<p>Those wait for you, curious and intrepid reader, in the attached
+<a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2019/dogon/apholife.c">apholife.c</a> file, which is a partially obfuscated version of the
+program I wrote with a lot of helpful annotations and comments for myself and
+posterity, revealing some of the magic under the hood. This program is also a
+somewhat improved version which uses <code>ldexp()</code>s in the draw routine and has
+bigger constants, so it can zoom up to level 1024 if memory allows, and it tries
+its best to avoid dumping core on the poor user when its memory runs out, rather
+it enters freeze mode where you can still travel in calculated frozen
+space-time. Well, it’s not nice and tame, it even has an escape key, usage
+message, and to top it all it even avoids <code>gets(3)</code>!</p>
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