re-add flat-mcmc
re-add flat-mcmc

simonmichael/stackage,massysett/stackage,mrkkrp/stackage,jonschoning/stackage,fpco/stackage,clinty/stackage,iand675/stackage,michalkonecny/stackage,soenkehahn/stackage,asr/stackage,athanclark/stackage,Daniel-Diaz/stackage,stackbuilders/stackage