Implemented GeoDistanceFacet.
Improved changes made in 9c8799f, allowing to pass kwargs to ES when using generate_model
Merge pull request #255 from dourvaris/master

GeoDistanceFacet implementation.
Merge pull request #256 from leo-naeka/master

Improved changes made in 9c8799f, allowing to pass kwargs to ES
Merged from aparo master