CLN: Assorted Cleanups
- make PTA/DTA strftime() return ndarray instead of Index
- fix a xfailed Series[Period] test
- avoid imports of Index subclass in arrays.categorical and arrays.datetimelike
- some typing
Hello @jbrockmendel! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



















There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-08-07 00:56:59 UTC thanks @jbrockmendel 