Improve HashSequencer performance by using -1 as the noEntryValue
Improve HashSequencer creation by going through factories with names.
Provide a bunch of new constructors
Improve ImmutableSequencerImpl efficiency by using -1 for the noEntryValue
Test that serialization works in the AbstractSequencerTest
Introduce additional ImmutableSequencer factories
Add serialization proxies to Sequencers that should halve the size of the serialized form
Make SequencerEntrySet and SequencerKeyList Serializable