Updated release note about GH4216.

BUG: legend was not displayed in `DataFrame.plot(kind='kde')`.
BUG: set name attr in DatetimeIndex and PeriodIndex

Now index names are preserved through slicing
BLD: use wheels and newer scipy bc of 33 scipy issue
TST: no need for flavor testing in skip

Skip bs4 tests when 4.2.0 is found.
TST: add message to nose.SkipTest
TST/CI: add scikits.timeseries wheel back
TST: properly skip html5lib
BLD: use wheels and newer scipy bc of 33 scipy issue
ENH: Add date_format keyword to to_csv()