Doc Bugs

[MichaelL@frogware.com]

I don't know if anyone cares about this, but there are two doc bugs in the
"Pattern Matching" documentation: first, one of the examples at the end
uses the old (?) "define-structure" form, rather than "define-struct";
second, the "$\$$" symbol in two of the examples should be replaced with "
$". (The written descriptions are correct, the examples seem to be out of
date.)

It would of course be nice if that doc was merged into the new MzLib doc...