Typo, there is no interp if input is not masked.
Cosmetics, just organizing the code.
Cosmetics, removing old comments.
find_closer_then now uses haversine distance.
Cosmetics, cleanning maud.py.
Defining AVG_EARTH_RADIUS & DEG2RAD.
haversine_scalar completely in cython.
haversine_scalar now returns type double.
Import sin and others from libc.math
Speeding up apply_window_mean_2D_latlon()
Speeding up apply_window_mean_2D_latlon_masked().
Using pi from libc.math.
Python wrapper for _haversine_scalar.

_haversine_scalar is only for inside module use, so haversine_scalar()
allows external calls.
Bugfix, apply_window_mean_2D_latlon_masked uses array.

apply_window_mean_2D_latlon_masked must normalize by the sum of the
weights once at a time. First it checks if are there valid numbers for
the positions that is normalizing.

The non masked version do not require that since will has at least one
valid value, itself.
Bugfix, apply_window_mean_2D_latlon_masked, only valid values.

First check if the data is not masked before sum.