BUG: Allow non-float values in get_yahoo_quotes.

Fixes issue: #5229
Merge pull request #8742 from dstephens99/issue5229

BUG: Allow non-float values in get_yahoo_quotes.
DOC: 15.1 release notes
RLS: v0.15.1 final
DOC: v0.15.2 whatsnew
BUG: Fix groupby methods to include *args and **kwds if applicable.
Update tutorials.rst

Add a pandas tutorial to the tutorial links.
Merge pull request #8758 from dstephens99/issue8733

BUG: Fix groupby methods to include *args and **kwds if applicable.
DOC: clean-up v0.15.1 whatsnew file
Merge pull request #8755 from jorisvandenbossche/doc-fixes2

DOC: clean-up v0.15.1 whatsnew file
Merge pull request #8759 from wavedatalab/patch-1

Update tutorials.rst
DOC: update sphinx version requirements
TST: Raise remote data error if no expiry dates are found (io.data.Options)
BUG: concat of series of dtype category converting to object dtype (GH8641)
Merge pull request #8763 from dstephens99/issue8761

TST: Raise remote data error if no expiry dates are found (Options)
Merge pull request #8714 from jreback/series_concat

BUG: concat of series of dtype category converting to object dtype (GH8641)
BLD: remove network tests from 3.2 build
BLD: fix 3.2 build
TST: Change a failing test #8768
BUG: concat of series of dtype category converting to object dtype (GH8641)