Feat/neighbors

[cwebear]

add neighbors and matchup files
matchup.py contains the nearest neighbor class, a bag for nearest neighbor parameters
neighbors.py contains 3 functions accociated to KDtree lookup :

to_seconds : Converting datetime64 to floating-point seconds since a fixed epoch and used to let the user set time delta in a datetime format.
spatial_nearest : returning indexes and asociated distance of stacked points between pointset and gridset
temporal_nerest : returning indexes and asociated timedelta of stacked points between pointset and gridset