ENH: support timedelta64[ns] as a serialization type in HDFStore for query and append (GH3577)
CLN: refactored locations of timedeltas to core/tseries/timedeltas (from a series of functions in core/common)
TST: add pandas/tseries/tests/test_timedeltas.py
API: add full timedelta parsing and conversion to np.timedelta64[ns]
ENH: add top-level to_timedelta to convert string/integer based to timedeltas
Merge pull request #4822 from jreback/timedelta_hdf

ENH/CLN: support enhanced timedelta64 operations/conversions
PERF: much faster to_datetime performance with a format of '%Y%m%d'
Merge pull request #4826 from jreback/dunit

PERF: much faster to_datetime performance with a format of '%Y%m%d'
BUG: enhanced to_datetime with format '%Y%m%d' to handle NaT/nan and NaT-like better
Merge pull request #4828 from jreback/dunit2

BUG: enhanced to_datetime with format '%Y%m%d' to handle NaT/nan better
TST: tests for GH4812 (already fixed in master)
Merge pull request #4813 from jreback/dup_resample

TST: tests for GH4812 (already fixed in master)