Tweak makefile recipe for pdfs

This commit adds '| ver' to the prerequisites for the textbook pdfs.  Now the version
info should be automatically generated when necessary.
Prettify urls

This commit removes the 'http://' from the urls in the textbook.
Release version 0.2.2

* Generate bibtex entry for the textbook and add to the book's
  preamble automatically.
* Remove the ugly 'http://' from the front of URLs.