BUG: disallow mixed dtype operations
PLAT: platform sorting issue surfaced with time_grouper
Merge pull request #6649 from pydata/platform_sort

PLAT: platform sorting issue surfaced with time_grouper
DOC: update groupby pd.Grouper docs
CLN: move set_grouper/get_grouper type pd.Grouper methods to internal
Merge pull request #6655 from jreback/groupby

DOC/API: pd.Grouper docs / api
Merge pull request #6652 from cpcloud/gh-5198-stack-blow-eval-mixed-type-operations

BUG: disallow mixed dtype operations in eval/query