ENH: print some progress when drawing walkers in MPI
ENH: print some progress when drawing walkers in MPI

guillochon/MOSFiT,bmockler/MOSFiT,villrv/MOSFiT,mnicholl/MOSFiT,guillochon/FriendlyFit,bmockler/MOSFiT,mnicholl/MOSFiT,mnicholl/MOSFiT,guillochon/MOSFiT,villrv/MOSFiT,guillochon/MOSFiT