small docstring tweaks
small docstring tweaks

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