emcee v3.1.1rc1

Added functionality to give a description in the progress bar (#401)

* Update pbar.py

* Update ensemble.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update ensemble.py

* Update pbar.py

* Update ensemble.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>