Regional sum / mean

[wwieder]

It would be nice to have examples for creating weighted sums & time series for:

• Regions (for specified bounding boxes)
• Arbitrary areas (e.g. shape files)

[wwieder]

example of regional masks for the ocean is here
https://pop-tools.readthedocs.io/en/latest/examples/region-mask.html#More-useful-region-masks

[jhamman]

Would also be worth looking at regionmask: https://regionmask.readthedocs.io/en/stable/