Updated after comments from @uboness to perform some renaming and remove dependency on InternalTerms base class as this had some irrelevant functionality. The relevant bits of InternalTerms were therefore copied into InternalGeoHashGrid.Bucket and interface created (GeoHashGrid) to hide InternalGeoHashGrid impl from clients.
Package name change from o.e.s.aggs.buckets.terms to o.e.s.aggs.buckets.geogrid