CLN: Add _reset_cache method to PandasObject
CLN/ENH: Make names getattr'able in core/ops +PEP8.

Now the name passed to a method can be used to get that method from the
NDFrame (previously you had things like `or_ [|]`. better to just have
them all be named exactly what they are s.t. subclasses can do
`getattr(super(self, MyClass), name)(*args, **kwargs)`.
Fixed assertion error message
DOC: fix building of gbq docs
Merge pull request #5242 from ojh/master

Fixed assertion error message
Merge pull request #5241 from jorisvandenbossche/docs-gbq-fixes2

DOC: fix building of gbq docs
API: default export for to_clipboard is now csv (GH3368)
Merge pull request #5070 from jreback/clip

API: default export for to_clipboard is now csv (GH3368)
TST: Added test for Excel writers with duplicated column names.

Test for issue #5235
Merge branch 'tst_excel_duplicated_cols' of https://github.com/jmcnamara/pandas into jmcnamara-tst_excel_duplicated_cols
API: add excel kw to to_clipboard to preserve compat behavior (related GH5070)
Merge pull request #5243 from jreback/clip2

API: add excel kw to to_clipboard to preserve compat behavior (related GH5070)
Merge pull request #5240 from jtratner/cleanup-core_ops

CLN/ENH: Make names getattr'able in core/ops +PEP8.
Merge pull request #5238 from jtratner/add-_reset_cache-to-PandasObject

CLN: Add _reset_cache method to PandasObject