CLN: add diff to series/dataframe groupby dispatch whitelist
StataWriter: Replace non-isalnum characters in variable names by _ instead of integral represantation of replaced character. Eliminate duplicates created by replacement.
Merge pull request #5719 from gdraps/groupby-dispatch-2

CLN: add diff to series/dataframe groupby dispatch whitelist
DOC: trim CONTRIBUTING.MD
Merge pull request #5721 from y-p/PR_contributing

DOC: trim CONTRIBUTING.MD
DOC: DatetimeIndex accepts name param
Merge pull request #5722 from TomAugspurger/datetimeIndex-name-doc

DOC: DatetimeIndex accepts name param
BUG: don't use partial setting with scalars (GH5720)
Merge pull request #5723 from jreback/empty_frame

BUG: don't use partial setting with scalars (GH5720)
Merge pull request #5709 from PKEuS/master

StataWriter: Replace non-isalnum characters in variable names by _ instead of integral represantation of replaced character. Eliminate duplicates created by replacement.
DOC: small doc build warning: Note -> Notes
DOC: add demo of factorize
Merge pull request #5726 from jorisvandenbossche/patch-1

DOC: small doc build warning: Note -> Notes
Merge pull request #5731 from unutbu/factorize-doc

DOC: add demo of factorize
CLN: cache indexers in internal_names_set (reported GH5727)
BUG: Bug in multi-index selection in PY3 when using certain keys (GH5725)
Merge pull request #5730 from jreback/repr_fix

CLN/BUG: indexing fixes (GH5725, GH5727)
TST: Cleanup temp files in Excel test.

Issue #5735
Merge pull request #5736 from jmcnamara/bug_excel_test_cleanup

TST: Cleanup temp files in Excel test.
BUG: raise KeyError if missing value in py3 on multi-index (GH5725), revisited