Gridding testing

[nannau]

Additions to the coordinate gridding with climpyrical:

• Handling coordinates and transforming coordinates into correct CRS
• Flattening coordinates into pairwise points
• Finds nearest indices of stations in coordinate grids
• Finds nearest indices of several stations in coordinate grids
• Finds the model value associated with a station, interpolates if no valid model value exists (i.e. station over water)
• Checks inputs of all the above functions
• Tests many new cases for above functions

[nannau]

@jameshiebert, @rod-glover and @nikola-rados could I get a LGTM from any of you on this PR when you get a chance?

I've addressed the following suggestions:

• Removed accidental .coverage file
• Remove return statement from all check functions
• Provide more detailed exception description guiding user on the error raised based on their inputs
• Added an additional check_ndims check function that ensures an array is of the expected size.
• Parameterizes the expected error to be found in the context manager with pytest.raises