DOC: add mention of idx* methods in max/min methods of Series/DataFrame

put mention of what the function does
BUG:  Fixed bug in reset_index with ``NaN`` in a multi-index (GH3586_)
DOC: add mention of argminmax in basics.rst
Merge pull request #3580 from cpcloud/argminmax-doc-3574

DOC: add mention of idx* methods in max/min methods of Series/DataFrame
Merge pull request #3587 from jreback/set_index_nan

BUG:  Fixed bug in reset_index with ``NaN`` in a multi-index (GH3586_)
TST: GH3579, period index misbehaving in groupby

BUG: fix take platorm issue with PeriodIndex (GH3579)
Merge pull request #3591 from jreback/groupby_period_index

BUG: fix take platorm issue with PeriodIndex (GH3579)