DOC: Fix typos in CONTRIBUTING.md
ENH: implement non-unique indexing in series (GH4246)

DOC: release notes
Merge pull request #4247 from jreback/series_dups

API: implement non-unique indexing in series (GH4246)
BLD: use mpl 1.1.1 in python 2.7 production travis build
Merge pull request #4243 from kjordahl/master

DOC: Fix typos in CONTRIBUTING.md
Merge pull request #4248 from cpcloud/mpl-1.1.1-build

BLD: use mpl 1.1.1 in python 2.7 production travis build
BUG: remove six import
Merge pull request #4250 from cpcloud/six-fix

BUG: remove six import
TST: no need for flavor testing in skip

Skip bs4 tests when 4.2.0 is found.
DOC: add v0.13.0.txt release notes file (but not to the index yet)
Merge pull request #4257 from cpcloud/read-html-flavor-attr

TST: no need for flavor testing in skip