working through issues.
Performing to spec with LegacyPairGenerator.

!!! FOR REALS !!!
Removed trace file.
Cleaning up move generators and removing commented code.
Renamed context generator and added support for early stopping.
Added code to automatically stop sampling when appropriate.
Merge branch 'sri-coref'
Removed unnecessary logs.
Cleaning up HierCorefDemo.
Added ++ and -- methods to BagOfWordsVariable for non-mutating addition and subtraction.
Added Entity Size Prior feature.
Added BagOfWordsSizePrior.
updated HierCorefDemo.
Added 'required' argument to CmdOption so that you don't need to override it to supply.
Added back in doCoreference method for KDD.
updated getTargetCoref to not fail when coref hasn't been set.