CLN refactor with _apply_to_column_groupbys
BUG: Fix wrong str.format() calls in Index.summary

GH3869
Merge pull request #4751 from jtratner/fix-summary-GH3869

BUG: Fix wrong str.format() calls in Index.summary
BUG: Fix crash using to_csv with QUOTE_NONE

Now passes `quotechar` to csv's writer. Default is same as csv (`'"'`),
but sets to `None` with `quoting=csv.QUOTE_NONE`.
Merge pull request #4752 from jtratner/fix-to_csv_QUOTE_NONE-GH4328

BUG: Fix crash using to_csv with QUOTE_NONE
CLN: Remove redundant call to get_splitter
ENH:  GH2578, allow ix and friends to partially set when the key is not contained
      in the object
API: iat/iloc will raise if enlargement is specified as its ambiguous

CLN: set_value in Series/Frame now go thru indexing routings in core/indexing.py
Merge pull request #4515 from jreback/partial_setting

ENH/API:  GH2578, allow ix and friends to partially set when the key is not contained in the object
CLN: Remove unused assignment
ENH:Add raise_with_traceback & use in assertRaises

* Adds `raise_with_traceback` to `pandas.compat`, which handles the
  Python 2/3 syntax differences for raising with traceback.
* Uses `raise_with_traceback` in `assertRaises` and `assertRaisesRegexp`
  so they provide better feedback.

ENH: raise_with_traceback method.
CLN: Better exceptions and tests for core/frame

CLN: Big simplification of test_frame
TST: Add test cases for bad input, etc.
CLN: Exceptions that shouldn't happen should be assertions (mostly _apply*)
CLN/TST: Right Exceptions + remove duplicate tests

A few tests were duplicating the same thing or actually just the same
test, those have been refactored or removed. Many tests were changed to
specify the Exception they were looking for (and also to use the new
`with_statement` format for assertRaises, etc.)

CLN: Harmonize SparseDF and DF Exceptions
ENH: SparseDF apply now accepts axis='columns'
BUG:  (GH2702) Bug with Series indexing not raising an error when the right-hand-side has an incorrect length
Merge pull request #4732 from jtratner/change-bare-exceptions-pt-3

CLN: Improve Exceptions in core/frame and testing in test_frame and test_multilievel
CLN: Move print_versions into pandas proper.

CLN: Make print_versions export a method

Make ci/print_versions call pandas/util/print_versions
Merge pull request #4760 from jtratner/add-versions-method

CLN: Move print_versions into pandas proper.
Merge pull request #4756 from jreback/nested

BUG/ER:  (GH2702) Bug with Series indexing not raising an error when the right-hand-side has an incorrect length
TST/CLN: moved the legacy tests out of tseries/test_timeseries.py to tseries/test_timeseries_legacy.py
BUG: (GH4758) Bug in multi-indexing with a partial string selection as one part of a MultIndex
Gotachas -> Gotchas