[FR] LonLat to EqualAreaGrid interpolation

This issue is related with #46 , but it is much harder.

Here the task is to interpolate from a LonLatGrid to a GaussianEqualArea grid, or some other kind of grid, and vice versa. For this we have to do several steps:

1. Create the underlying Equal Area grid based on given user input (probably given approximate square meters)
2. Interpolate.

The difficulty is, I do not know how to do either of these, as I do not know how to do interpolation in non-regular grids, nor how to define well equal area grids.

I know that CDO does this, and I also know that the most easy grid to do this in is the Gaussian grid, GaussianEqualArea. The source code that loads gaussian equal area grids from CDO, ClimArray_eqarea, knows how to transform the given latitudes to a full longitude-latitude coordinate, but we would need to generate the initial latitudes as well. If god can help you find where in the source code of CDO this is done, then we can use it...

Of course, we have to be a bit careful here. We can't directly copy the source code of CDO, because we want this package to remain MIT licensed.

Start by reviewing the related issue #46 and the existing ClimArray_eqarea source that loads Gaussian equal-area grids. Research how CDO defines GaussianEqualArea latitudes and how interpolation is handled for non-regular grids, while checking that any reference implementation is compatible with the MIT license. Done means supporting interpolation between LonLatGrid and an equal-area grid created from user input.