The pdf for Pickaxe-2 is missing some important hyperlinks I was expecting
it to have. e.g.

p424:
class Class < Module : The "Module" should hyperlink to its definition.

p 480:
Subclasses: Bignum, Fixnum: should also hyperlink

Looks like the PDF generator missed some categories of links. Can these be
fixed at some point in the PDF? Will purchasers get PDF updates?

Thanks!