Minimal dependencies

[jules-ch]

Hey there,
It might be nice to have a minimal implementation with extra dependencies.

For specific usecases, I'm using only aggregations and joining between datasets on grid index.

I'd see a minimal dependency without pooch, matplotlib etc that only uses core capability.

[keewis]

I can see this being useful, but I'd probably delay this until we can promise a bit more stability (but either way I'll bring this up in the dev meeting next week).