Work

thanks for this  -- I'll be cross-referencing sections for my Radiation/Remote Sensing course:
http://clouds.eos.ubc.ca/~phil/courses/atsc301/index.html

the changes in this branch add png files for the html build, e.g.:

http://clouds.eos.ubc.ca/~phil/djpine_python/Book/_build/html/chap5/chap5_plot.html