FIX raise when groupby selecting cols not in frame
PERF: dataframe.from_records: read into list w/ itertools.islice when specifying nrows #6700
DOC: fixes empty boxes + too wide:
- excel: code snippets too wide
- visualisation: for some reason now empty boxes when ipython code blocks with plt.figure were suppressed, but not when removing the semicolon
DOC: improve docstring of pd.melt
PRF: .shift() speedup: Only pass in c_contiguous arrays to np.roll/take
PRF: Fixed shift speed tests and added consolidated DataFrame shift perf
test
BUG: fix NDFrame.as_blocks() for sparse containers

SparseBlocks don't consolidate, so previous implementation silently
dropped all but the last blocks for given dtype.

Also, drop the 'columns' kwarg, there's reindex for that.
Merge pull request #6747 from dalejung/quick_shift_fixes

Quick shift fixes
Merge pull request #6748 from immerrr/fix-as-blocks-for-sparse

BUG: fix NDFrame.as_blocks() for sparse containers
BUG: NaTType can be unpickled properly
Fix SQLLegacy to allow parameters as mapping
Add SQL read_parameters tests
Merge pull request #6709 from gpoulin2/master

BUG: Allow mapping as parameters for SQL DBAPI2
Merge pull request #6746 from jorisvandenbossche/doc-fixes

Doc fixes
PERF: perf improvements in timedelta conversions from integer dtypes
DOC: documented that .apply(func) executes func twice on the first time

Related issues are #2656, #2936 and #6753.
Merge pull request #6756 from anton-d/master

DOC: documented that .apply(func) executes func twice on the first time
Merge pull request #6754 from jreback/timedelta_perf

PERF: perf improvements in timedelta conversions from integer dtypes
DOC: correct alignment of GH6756
BUG: Series.iteritems should be lazy