Entropy calculation

http://tkhanson.net/cgit.cgi/misc.git/plain/entropy/Entropy.html

http://arxiv.org/pdf/0808.1771v2.pdf

http://vserver1.cscs.lsa.umich.edu/~crshalizi/notabene/cep-gzip.html

http://www.gzip.org/deflate.html

http://log.brandonthomson.com/2011/01/quick-python-gzip-vs-bz2-benchmark.html

http://www.gzip.org/deflate.html