Ben Pierce

Hi @kanderso-nrel oh, I forgot that those are in `shading.py` already. That probably makes more sense; I can add a new module `topography.py` or something like that later on for...

@kanderso-nrel @jsstein OK, I added a test that downloads the DEM and then verifies that three hardcoded points are the same elevation. I had the function place the downloaded file...

@kandersolar @jsstein The horizon functions in this PR have been updated and appear to have no conflicts. I think I did the tests look right, but they could use a...

@cwhanse done, it seems like [docs/sphinx/source/api.rst](https://github.com/pvlib/pvlib-python/blob/master/docs/sphinx/source/api.rst) no longer exists, is there a replacement or somewhere else to modify?

@cwhanse done, thanks! The checklist should be up to date, then.

@kandersolar ok, removed all the DEM and shading stuff, now only the pvgis horizon method is added here ([diff](https://github.com/pvlib/pvlib-python/compare/main...bgpierc:pvlib-python:add_horizon)). I think we should be good to go now.

@AdamRJensen Setting `horizon_azimuth` to the index makes sense to me, done

Ok, I had it return the meta data from PVGIS as well. I'm not sure if we want to make the function return a `Series` rather the a `DataFrame` as...