ENH: Add usecols option to python parser.

Closes #4335

Added release note and fixed py3 compat

Updated docs for consistency
add ScatterPlot class to allow df.plot(kind=scatter)
API/CLN: consolidate truncate into NDFrame (panel had a separate method)
API: truncate error if before > after is now a ValueError (rather than AssertionError)
Merge pull request #5244 from jreback/truncate

API/CLN: consolidate truncate into NDFrame (panel had a separate method)
BUG: fixed issue with drop on a non-unique index with Series (GH5248)
CLN: remove reindex_like from core/frame.py (use core/generic.py version)
Merge pull request #5249 from jreback/drop_dup

BUG: fixed issue with drop on a non-unique index with Series (GH5248)
Merge branch 'scatterplot' of https://github.com/zachcp/pandas into zachcp-scatterplot
API: allow Series/Panel dropna to accept other args for compat with DataFrame (GH5233/GH5250)
DOC: core/generic/drop docs from array-like to list-like
Merge pull request #5251 from jreback/dropna

API: allow Series/Panel dropna to accept other args for compat with DataFrame (GH5233/GH5250)
Merge pull request #5252 from jreback/drop_dup2

DOC: core/generic/drop docs from array-like to list-like
DOC/TST: core/generic/drop doc-string and tests
Merge pull request #5211 from guyrt/issue-4355-usecols-python-engine

ENH: Add usecols option to python parser.
Merge pull request #5253 from jreback/drop3

DOC/TST: core/generic/drop doc-string and tests
ENH/API: Accept DataFrame for isin

API: Series should respect index labels.

DOC: Update what's new to use a DataFrame

API: Remove iloc argument to isin.
DOC: core/generic/drop doc-string change
Merge pull request #5199 from TomAugspurger/isin_dfs

ENH/API: Accept DataFrame for isin
CLN: Fixups to exceptions in generic

Improved message and better exception types.