Added warning about serialized object and removed beta.
Added warning about serialized object and removed beta.

Right now I don't think we want to guarantee compatibility of
serialized object between versions (although they will likely
work fine). We can revisit this as we clarify our versioning.

ecliptical/GeoIP2-java,ecliptical/GeoIP2-java,CASPED/GeoIP2-java,maxmind/GeoIP2-java,maxmind/GeoIP2-java,CASPED/GeoIP2-java