Ensure and test consistency between surface portions of algorithms

[allisonrenie]

Ensure that surface irradiance produced by attenuate_all matches surface irradiance produced by attenuate_surface

[allisonrenie]

Added testing for this in branch #44 , did find differences between surface algs, as expected. The differences are now documented in the testing structure, so changes can be monitored.

What to do about the differences is still somewhat unclear. I think at the moment the best thing to do is just to alert the user of the differences and let them decide.