BUG: (GH3601) Reindex data if reordering time/period index
Merge pull request #3619 from dieterv77/FixGH3601

BUG: (GH3601) Reindex data if reordering time/period index
DOC: correct mpl_style option name in whatsnew.html GH3640
DOC: CONTRIBUTING.md
try out string iter
use slicing syntax
ENH: add Series.str iterator