added _propose_position method
added _propose_position method

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