A geospatial index

This code provides an index for object proximity. The index structure is based on S2 Geometry, and this code uses the github.com/golang/geo implementation.

The primary method is Update, which takes a publisher's opinion about the set of possible positions, each with an associated probability, for an object key in the publisher's namespace. Input also includes the identifier for data the publisher used to generate this input. Update returns the set of obsolete conjunction reports (if any) and a set of new conjunction reports (if any). This method also returns the id (if any) the publisher previously used for the object key.

This implementation is not safe for concurrent use.