Add automatic generation of citation info

This commit adds a command to the Makefile to generate a BibTeX record for the
book; it also adds that information to the front page of each document so that
people will (hypothetically) know how to cite it.  I expect the lack of author
and the versioning info to confuse most people.
Update bibtex record keys to AutYY

Using an underscore in the bibtex record keys was conflicting with TeX input
for the unicode characters in Emacs, so I'm removing the underscore.
Debug recipe to produce citation info

A flag to 'echo' was appearing in the CITATION file, so I've removed it.  The
recipe seems to work now.
Merge branch 'master' into dev

Conflicts:
	asymptotics.tex
	finitesample.tex
	linearregression.tex
	probability.tex
Undebug citation information generation

'echo' really does need the -e flag for generating the bibtex info; this commit
adds it back in.
Remove 'Version' from date list

The version tags are going to start having 'v' in front of them, so including the
word 'version' where they're listed is redundant.
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.