added mongodb river
Merge pull request #280 from offerpop/mongo-river-keepjdbc

added mongodb river
Handle zero-size term facets. Fixes #282.
Merge pull request #283 from danfairs/hotfix/282-zero-size

Handle zero-size term facets. Fixes #282.
Bugfix: size set to 0

setting the size in a search to 0 (not None) leads to used size of 10
in the query. This is not what it should do. If the resultset 0 is
wanted it should query it.
Merge pull request #284 from julianhille/master

Bugfix in setting the size to 0 in a search
Fix __init__ of GeoDistanceFilter optimize_bbox