Add return info for run_mcmc
Add "resume" functionality to run_mcmc
Add test for run_mcmc resumption
change to using reset to reset _last_run_mcmc_result (and initialize)
Merge branch 'add-memory-of-last-run' of https://github.com/eteq/emcee into eteq-add-memory-of-last-run
incorporating @ipashchenko's comment
Merge branch 'eteq-add-memory-of-last-run'