TST: suppress gratuitous warnings
ENH/TST/DOC: Implement experimental io.excel._Openpyxl2Writer
VIS: Hide labels for NaN/zeros in boxplt

[ci skip]
Merge pull request #7565 from neirbowj/openpyxl2_issue7177

ENH: Implement _Openpyxl2Writer for pandas.io.excel
DOC: v0.15.0.txt edits
PERF: add copy=True argument to pd.concat to enable pass-thru concats with complete blocks (GH8252)
Merge pull request #8331 from jreback/concat_copy

PERF: add copy=True argument to pd.concat to enable pass-thru concats with complete blocks (GH8252)
CLN: pep8 clean up of sql.py
TST:  test_precision_conversion on windows fix (GH8324)
Merge pull request #8340 from jorisvandenbossche/sql-pep8

CLN: pep8 clean up of sql.py
DOC: move trellis under visualization.rst
BUG: Work-around openpyxl-2.1.0 NumberFormat removal
Merge pull request #8356 from jreback/excel_fix

BUG: Work-around openpyxl-2.1.0 NumberFormat removal
ENH/BUG: allow timedelta resamples
Merge pull request #8345 from jreback/resample

ENH/BUG: allow timedelta resamples
DOC: timedelta resample docs
Merge pull request #8353 from TomAugspurger/trellis-doc

DOC: move trellis under visualization.rst
BUG: Bug in alignment with TimeOps and non-unique indexes (GH8363)
Merge pull request #8364 from jreback/datetime_ops

BUG: Bug in alignment with TimeOps and non-unique indexes (GH8363)
BUG: rolling_window() properly averages weights in mean=True mode; removed scikits-timeseries dependency for testing; added further tests for rolling_window()