DOC: add basic documentation to some of the GroupBy properties and methods
DOC: add GroupBy class to api.rst
DOC: add import for GroupBy object to api.rst
DOC: add GroupBy.aggregate and GroupBy.transform to api.rst
DOC: add meta comment to api.rst about when GroupBy objects are created
DOC: add links to api.rst
Set basic stacklevel for SettingWithCopy warning
Merge pull request #5581 from jtratner/fix-stacklevel-for-basic-setting

CLN/BUG: Fix stacklevel on setting with copy warning.
Truncate repr by default rather than changing to info view.

Truncate wide HTML repr rather than changing format.

Truncate HTML repr for DataFrames with MultiIndex-es

Add tests for long & wide Dataframe HTML reprs

Remove now-dead code for info display in HTML repr.

Fix HTML repr of wide tables with named indices

Make plain text repr follow HTML repr, truncating large DataFrames

Fix up tests for string repr

Update docs for DataFrame reprs

Add an option to switch back to info repr for large DataFrames
Add repr footer showing total number of rows and columns
Use to_string() to format DataFrames for clipboard.

Using str() has some unhelpful properties, especially when DataFrames
are large enough that the default repr does not show them in their
entirety. The defaults for to_string() are more helpful for the
clipboard.

Closes gh-5346
Update FAQ entry on controlling repr
Fix typo
Merge pull request #5587 from Bklyn/master

Fix typo
Explain repr changes more prominently in release notes
Merge pull request #5550 from takluyver/long-repr-html

HTML reprs for large dataframes.
BUG: to_html doesn't slice index to max_rows before formatting
VB: add to_html vbench
Merge pull request #5589 from y-p/PR_fix_slow_truncated_large_repr_html_5588

BUG: to_html doesn't slice index to max_rows before formatting
PERF: perf enhancements in indexing/query/eval
Merge pull request #5590 from jreback/indexing_perf

PERF: perf enhancements in indexing/query/eval
BUG: Bug in groupby returning non-consistent types when user function returns a None, (GH5592)
Merge pull request #5593 from jreback/groupby_apply

BUG: Bug in groupby returning non-consistent types when user function returns a None, (GH5992)
Add image for whatsnew docs
TST: dtype issue in test_groupby.py on windows