Investigate the feasibility of developing a GVAL accessor for xarray.

[fernando-aristizabal]

Investigate how a GVAL accessor for Xarray would work.

• Investigate here.
• How would accessor methods work in their return types? Under what circumstance would we lose the gval accessor?
• What methods and attributes would we want to the accessor to have??
• Should we let them know based on their suggestion ("To help users keep things straight, please let us know if you plan to write a new accessor for an open source library.")
• Investigate extended projects that have accessors already to see how they are written.
• Investigate tools that make documenting accessors easier.