DEPS: Added tz keyword to to_datetime function, deprecates utc
- [x] closes #13712
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
Hello @harpolea! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on September 01, 2017 at 13:50 Hours UTC note that we just merged: https://github.com/pandas-dev/pandas/pull/17109

so rebase In general, I am wondering whether it is actually needed to deprecate the keyword / worth the trouble for all impacted users. 
I am certainly + 1 on adding tz keyword. But we can keep utc=True just as an alias for tz='utc' why don't we put a DeprecationWanring on  utc rather than a FutureWarninhg

kind of a soft deprecation  can you rebase / update can u rebase and move note to 0.22 can you rebase / move note to 0.22.0 closing as stale, but if you'd like to keep working, ping and we can reopen