pfdf 3.0.0

This release adds the `data` package, which provides routines to download commonly used datasets from the internet. The release also provides pfdf tutorials as Jupyter Notebooks, improves array broadcasting in the `gartner2014` and `staley2017` modules, and introduces the `RasterMetadata` class (which manages raster metadata without loading data arrays to memory).

Documentation: https://ghsc.code-pages.usgs.gov/lhp/pfdf/
Release Notes: https://ghsc.code-pages.usgs.gov/lhp/pfdf/resources/release-notes/3.0.0…