Fixing bugs for CMAC VAP script to work
Fixing bugs to get MMCG working
ENH: updated ball_tree to new version in scikit learn
ENH: map_to_grid function and test

map_to_grid can use either ckdtree or balltree to perform lookups
DOC: initial map documentation
Merge pull request #47 from jjhelmus/master

ENH : map_to_grid function

The map_to_grid function created a Cartesian map from one or more radar objects.

* can use either a k-d tree or ball tree for fast neighbor lookup.
* documentation and tests included.
* support for mapping multiple radar untested and known broken if copy_field_data = False, this will be fixed next week.