compute cumulative radiant energy at Long/Lat over time range

demo function computes car's cumulative received solar energy over
course of race from 6/27 to 6/29. I assume we can charge from 10AM to
5PM, correct me if otherwise

also function to convert geographical coordinates to spherical

misc documentation

also we now depend on numpy, scipy, and matplotlib (and obviously still
python 3.3). install these