Bug in utils.coords_to_merit_tile

[jsta]

This returns n30w150 (a non-existent tile):

utils.coords_to_merit_tile(-121, 41)

it should return n40w125

[jonschwenk]

After looking at that function, and given this error, I would probably rewrite it to use geometries and an intersection() function from geopandas. Not sure how much slower that would be, but there aren't that many merit tiles, and it would be way more readable.