gif from matplotlib

http://www.jamesphoughton.com/2013/08/23/making-gif-animations-with-matplotlib.html
https://studywolf.wordpress.com/2013/09/20/python-visualization-with-matplotlib/
http://qiita.com/HirofumiYashima/items/51d8dac9a784de356c5b
http://cflat-inc.hatenablog.com/entry/2014/03/17/214719