added prune-bin flag to preserve beam search binning information
partially implemented margin data structures
implemented margin-violation code, but removed multiple violation. TODO: implement parallel violation so that we would collect: the node with max-margin + other non-dependent nodes.
added hinge-loss based learner
added PA-I
serious bugfix for clearning internal data after learning
updated NEWS
implemented violation-fixing learning
separated violation margin computation
implemented margin based learning
re-implemented learning code, especially to handle variety of learning algorithms
reorganize learning related parameters