Reword the recent deobfuscation changes

In most cases the word was changed to 'obfuscation' as it was about
obfuscation, not deobfuscation. In some cases like 1995/leo since the
file was (in 1995/leo) about a secret switch it was changed to
'secret.md' (and 'secret.html') but there were others like that as well.

One entry had the words 'spoiling the size rule' but this had been
changed to 'deobfuscating the size rule' which was obviously wrong.

In the latter YYYY/README.md files the judges had written after some
entries (brief summaries) '...

    ...We'll stop spouting spoilers now. Have fun exploring all the
    entries!

but that was changed to:

    ...We'll stop spouting deobfuscation information now. Have fun
    exploring all the entries!

which wasn't really about deobfuscation but just a brief summary of what
the entries did.

And in the most problematic case (at least for me :-), 2018/ferguson) I
had put a joke in:

    ... but it's the only Easter egg I won't spoil

but it was changed to 'won't deobfuscate' which not only is not what it
is but it spoilt the joke.

In some cases the word was changed back to 'SPOILER' (or similar) but in
most cases not. I believe it should be better now. There are some
caveats, however, as below.

Although make find_missing_links is okay I do not remember if this will
catch links that refer to '%%REPO_URL%%' or other pandoc tokens. This
means I might have to go back to some earlier years to verify links are
okay. That should not take that much time I hope.

It might also be that some wording can still be improved some but it is
hoped this will be discovered when checking links and looking over the
manifest (which obviously changed).

2018/burton1/index.html

@@ -432,12 +432,12 @@ It adds several nice-to-have features, and allows salt-to-taste customizability.
 <li>X86-FreeBSD 10.3, clang 3.4.1, -O0 and -O3</li>
 <li>TCC 0.9.26 (x86-64), used as a proxy for <a href="../../2001/bellard/index.html">2001/bellard</a></li>
 <li>UNIX V7 pcc (Johnson’s C compiler) on a <a href="http://simh.trailing-edge.com/">simulated PDP-11/45</a>
-(see the “<strong>DEOBFUSCATION</strong> section below for further detail)</li>
+(see the “<strong>SPOILER</strong> section below for further detail)</li>
 </ul>
 <div style="margin-bottom:60em;margin-top:4em">
-<strong>Deobfuscation information below; scroll down.</strong>
+<strong>Spoiler below; scroll down.</strong>
 </div>
-<h3 id="deobfuscation">DEOBFUSCATION:</h3>
+<h3 id="spoiler">SPOILER:</h3>
 <p>This started life as a personal challenge: write the shortest hex dump utility
 in C.</p>
 <p>The self-imposed ground rules in the hunt for shortest:</p>
@@ -514,12 +514,12 @@ and it is more interesting to remove characters by changing code than by filteri
 <a href="../../1986/bright/index.html">1986/bright</a> is similar in function,
 but it uses more characters in just setting up its obfuscation than this entire
 solution!</p>
-<h3 id="more-deobfuscation">MORE DEOBFUSCATION:</h3>
+<h3 id="bigger-spoiler">BIGGER SPOILER:</h3>
 <p>If you are unhappy with the way DEL (character 127) is handled,
 replace the cryptic expression <code>4&lt;(4^l&gt;&gt;5)?l:46</code> with <code>32&gt;l|l&gt;126?46:l</code>.
 Both take the same number of characters, but the former is a bit more interesting.
 Bonus question: how does the first expression work?</p>
-<h3 id="even-more-deobfuscation-and-some-history">EVEN MORE DEOBFUSCATION (and some history):</h3>
+<h3 id="biggest-spoiler-and-some-history">BIGGEST SPOILER (and some history):</h3>
 <p>Technically, <code>char o[0];</code> is illegal (SS 6.7.6.2) according to ISO (N1570). And
 <code>char o[];</code> is a conditionally supported feature (SS 6.7.6.2, 6.10.8.3).
 However, it works in modern C implementations as an extension, including GCC,