Add bcast collective operation to the MPIPool class
Add bcast collective operation to the MPIPool class

drphilmarshall/emcee,dfm/emcee,ipashchenko/emcee,farr/emcee,johnbachman/emcee,willvousden/emcee,dfm/emcee3,dfm/emcee,ga7g08/emcee,pkgw/emcee,johnbachman/emcee,linan7788626/emcee,elkingtonmcb/emcee,joezuntz/emcee,willvousden/emcee,jellis18/emcee3