Ensure that we can get a commit number from git

Currently, git describe fails with "fatal: No names found, cannot describe anything."
Merge pull request #5520 from invisibleroads/patch-2

Ensure that we can get a commit number from git
BUG: Bug in getitem with a multi-index and iloc (GH5528)
Merge pull request #5529 from jreback/iloc_mi

BUG: Bug in getitem with a multi-index and iloc (GH5528)
CLN: PEP8 cleanup
Merge pull request #5038 from alefnula/pep8

CLN: PEP8 cleanup
CLN: More autopep8
PERF faster head, tail and size groupby methods