More tightly modularize resources/ folder

[paulf81]

Currently in resource folder is:

• hercules/resource/upsample_wind_data.py
• hercules/resource/wind_solar_resource_downloader.py

This issue captures the intention that these elements could be broken down into clearer modules (collecting maybe some of the other sub-issues of this parent issue). One idea:

• A module file for downloads of particular points
• A module file for downloads of areas with resolution
• A module for conversion into Hercules format
• A module for upsampling in time and space

[paulf81]

#246 is now the first step in this process