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).

README.html

@@ -484,12 +484,12 @@ the top of the index.html for each entry as well. Keep in mind that C compilers
 often have bugs, or features which result the program failing to compile. You
 may have to do some syntax changing as we did to get old programs to compile on
 strict ANSI C compilers.</p>
-<p>Last, read the judges’ remarks and deobfuscation information on the program. Hints for <code>foo.c</code> are
+<p>Last, read the judges’ remarks (and sometimes spoilers) on the program. Hints for <code>foo.c</code> are
 given in <code>index.html</code>. Often they will contain suggested arguments or
-recommended data to use. Authors also sometimes provide deobfuscation information
+recommended data to use. Authors also sometimes provide obfuscation information
 about their entries.</p>
 <p>If you do gain some understanding of how a program works, go back to the source
-and reexamine it using some of the techniques outlined above. See if you can
+and re-examine it using some of the techniques outlined above. See if you can
 convince yourself of why the program does what it does.</p>
 <h2 id="regarding-the-source-archive">Regarding the source archive:</h2>
 <p>Each subdirectory contains all the entries for a single year. Often the file