added parallel_hash to support tuples of ndarrays
renamed pyhsmm.parallel import
broke out parallel methods for easier extension
broke out more parallel methods for extension
made sample_discrete_from_log_2d_destructive more numerically robust
fixed broken sample_discrete_from_log_2d
broke out parallel cost function
added copy_sample explicitly in intnegbin models
only run parallel setup code on first import
reworked parallel abstractions