improvements to time

time calculation now Mostly in terms of integer Unix Time, rather than
the heavyweight datetime.datetime class. We passed the heliophysics
unit test, but i'll check the prediction of cosTheta() tomorrow at 1PM
(i.e. solar noon-ish. damn Daylight Savings Time)

we need another function to generate proper Unix Time arrays for a
given day / timerange, to feed into cosTheta(). Also, we should treat
negative cosTheta output as 0, for array power purposes