python bindings for fregrid

[raphaeldussin]

Is your feature request related to a problem? Please describe.

fregrid is extremely useful as remapping tool but since it is written as standalone code, it
does not interface easily in a python workflow.

Describe the solution you'd like

It would be very beneficial to refactor fregrid as a library and add python bindings so
the remapping could be called with python, operating on an array and returning the
remapped array rather than manipulating files.

Describe alternatives you've considered

xESMF/ESMpy operate with this approach and are very widely used.