BUG/TST: wrong parsing of microseconds with format arg (#4152)
Merge pull request #4166 from jorisvandenbossche/bug-microsecond-parsing

BUG: wrong parsing of microseconds with format arg (#4152)
DOC: minor io/whatsnew doc edits
TST: to_datetime format fixes

CLN/TST: to_datetime cleanup

TST: tests for dayfirst=True
Merge pull request #4168 from cpcloud/sktimeseries-dl-fix

BLD: use the wheel url for scikits timeseries
Merge pull request #4167 from jreback/dt_format

TST: to_datetime format tests
BUG: series timedelta arithmetic was not being converted to ns