* add _to_radians and is_rad to convert only if necessary
* prefix all functions with get_
* add get_f_sky_pv, get_poa_sky_pv, get_ground_angle_tangent,
get_f_gnd_pv, get_f_gnd_pv, get_poa_gnd_pv, etc.
* update API ui

Signed-off-by: Mark Mikofski <[email protected]>

…irradiance

…t defined

* get_irradiance, output ordered dict or dataframe
* finish updating get_poa_global_bifacial to transpose beam and diffuse
for each side separately

…ion"

- use tan(zenith) in solar projection math latex
- implement gcr_prime and ground-sky-angles calculations
- add stub for ground-diffuse view factor

Signed-off-by: Mark Mikofski <[email protected]>

…o infinite_sheds

- calculate ground-sky angles to previous and next rows, assuming height
 is nonzero
- calculate limits on ground where it can see the sky
- calculate the view factor as a function of z on the ground to the sky
- fix places where it still says degrees, bad, no!
- add fixme for pv-sky view factor, still has wrong formula
- add tests for angles from point z on the ground to tops of current
 row, and limits of previous and next rows
- add a script to make the plot of ground-sky view factor versus z

- add comments, change names x->z
- add TODO's to limit number of rows, and set row-type: 'first', 'last',
or 'middle'

- was difference of angles, should be difference of cosines
- also add TODO's to return VF versus point x on panel, and don't use
averages

- change calc_fx_sky to calc_fz_sky since z is for ground and x is for
pv surface
- add docstring to calc_fz_sky and for ground_sky_diffuse_view_factor

* change _bigz() to just return bigz
* create a test figure of integrated vslue

…o infinite_sheds