Speed up DatetimeConverter by using Matplotlib's epoch2num when possible.
Added vbench performance benchmark for speed up of DatetimeConverter.
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
Fixes to DatetimeConverter speed up following PR comments and corresponding note in release notes..
Fix failed tests when importing Series from pandas.
Merge pull request #6650 from agijsberts/speed-up-dateconverter

PERF: Speed up DatetimeConverter by using Matplotlib's epoch2num when possible...
PERF: Improve performance custom business days (#6584)
REGR: fixing Timestamp/Series subtraction, resolves #6648
BLD: update wheel build script to add in psycopg2 support
Merge pull request #6592 from bjonen/master

Improve performance for custom business days (GH6584)
Merge pull request #6657 from rosnfeld/issue_6648

REGR: fixing Timestamp/Series subtraction, resolves #6648