Utility to load topography

[gmaze]

Being to able to easily load local topography will be very useful for plotting or QC methods.
This PR will provide a new method to do this.

New API:

    from argopy import TopoFetcher
    box = [-75, -45, 20, 30]
    ds = TopoFetcher(box).to_xarray()

This will help for euroargodev/terrain-following#1

[ocefpaf]

I have a similar prototype for a stand alone package for this (but I was using etopo2 instead). Do you think it would be better to factor it out in its own pkd so other packages can depend on it?

The downside is a slower development pace and higher maintenance cost.

[gmaze]

Do you think it would be better to factor it out in its own pkd so other packages can depend on it?

In theory, I would agree
In practice this would lead to another dependency to manage and sustain
So I would promote the idea of a simple function/method to be easily/freely copied/pasted from one library to the other

[ocefpaf]

To be honest I was on the fence and that is why I never published my version :-)

Sounds like a good plan!

[gmaze]

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