Added debug logging to synchronous execution loop.
Added memory efficient data graph vertex.

Can save a lot of memory if certain assumptions are met.
Renamed signals map to most recent signals map.
Exposing IntHashMap values.
Easier ClassTag specification for MemEffVertex.
Changed default kryo serializer pool size to 40.
Fixed conceptual problem and bug in SplayIntSet.

Added more comments and simplified the general structure.
SplayIntSet benchmarking facilities.
Merge branch 'master' into scala-2.11-akka-2.3.2-migration