Feature/split out resources

[paulf81]

PR #221 implemented a refactor of the resources module, but because included both file changes, and movement from a monolith file into seperate files, was hard to review because the specific changes were hard to observe.

This PR starts a more incremental approach by for now only splitting out the contents of hercules/resource/wind_solar_resource_downloader.py into seperate module files, without any additional changes except for correcting the imports. Specifically starting from:

download_nsrdb_data (lines 36-224) -- NSRDB via rex/HSDS
download_wtk_data (lines 227-403) -- WTK via rex/HSDS
download_openmeteo_data (lines 406-670) -- Open-Meteo HTTP API
plot_timeseries (lines 673-706) -- shared by all three
plot_spatial_map (lines 709-820) -- shared by all three
get_variable_label (lines 823-851) -- shared by all three
get_variable_colormap (lines 854-882) -- shared by all three

Move to:

hercules/resource/
  __init__.py                          # NEW - package init, re-exports public API
  resource_utilities.py                # NEW - shared plotting (4 existing funcs, moved as-is)
  nsrdb_downloader.py                  # NEW - download_nsrdb_data (moved as-is)
  wtk_downloader.py                    # NEW - download_wtk_data (moved as-is)
  openmeteo_downloader.py              # NEW - download_openmeteo_data (moved as-is)
  upsample_wind_data.py               # UNCHANGED

And then only make changes where these are imported in examples and discussed in docs. This way future modularization changes, as in #221 can be implemented without also including movement of code between files. (Specifically #221 moves repeated code blocks within the download scripts into new shared functions and that is not done here. The individual functions are moved as is)

[genevievestarke]

Hi @paulf81, this looks great! Would you be able to adjust one of the resource examples to show how the sub package is loaded/works?

[genevievestarke]

Looks great!