LOWTRAN Solar Irradiance, Horizontal User Data, and Transmittance models updated

SolarIrradiance.py is a LOWTRAN model accessed through Python of Solar Irradiance, as well as transmittance ground-space.

Lowtran solar irradiance model

Lowtran solar irradiance model and transmittance.

Also added was the user data mode, where your own measured temperature, pressure, humidity, etc. can be used to compute the transmittance spectrum more accurately.

Lowtran user data input model

Lowtran transmittance using user-provided data for model inputs.

Lowtran user data input model

Lowtran solar up-radiance using user-provided data for model inputs.