fix HTML problems associated with leading ---'s

Please do not use "**---**" in markdown lines to separate sections.

This causes `pandoc(1)` to generate "**\<hr />**".

The "**\<hr />**" has no effect in standard HTML 5 and interacts
badly with unquoted attribute values.

If a horizontal line is really needed, use "**\<hr>**".

If a short line is needed, use: "**\<hr
style="width:10%;text-align:left;margin-left:0">**"

1998/df/index.html

@@ -237,13 +237,13 @@ rot13 spoilers since it is somewhat complicated on a Mac to
 reverse them. Anyone out there should have enough discipline and
 rot13 shouldn’t be required, really. After all, we are not children
 anymore :-)</p>
-<hr />
+<hr style="width:10%;text-align:left;margin-left:0">
 <p>This paragraph is not part of the author’s remarks, but is a helpful
 gift from the judges; if you read too fast to stop yourself, this should
 give you enough time to stop, which you really need to do RIGHT NOW if
 you don’t want to read the spoilers, which really do spoil everything,
 we mean it.</p>
-<hr />
+<hr style="width:10%;text-align:left;margin-left:0">
 <p>The source file needs to be present because the words are read from
 it. The wordlist is encoded within the source using a 24 entry
 sliding dictionary where lowercase letters are offsets into the