Hand written ISO parser for Timedelta construction

[WillAyd]

• closes PERF: Hand Written Parser for Timedelta ISO 8601 Construction #19103
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Running 16 total benchmarks (2 commits * 1 environments * 8 benchmarks)
[  0.00%] · For pandas commit hash 76475dd8:
[  0.00%] ·· Building for conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt...............................................................
[  0.00%] ·· Benchmarking conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[  6.25%] ··· Running timedelta.TimedeltaConstructor.time_from_components                                      15.4±0.4μs
[ 12.50%] ··· Running timedelta.TimedeltaConstructor.time_from_datetime_timedelta                              8.06±0.3μs
[ 18.75%] ··· Running timedelta.TimedeltaConstructor.time_from_int                                             6.24±0.2μs
[ 25.00%] ··· Running timedelta.TimedeltaConstructor.time_from_iso_format                                      12.1±0.4μs
[ 31.25%] ··· Running timedelta.TimedeltaConstructor.time_from_missing                                        2.07±0.03μs
[ 37.50%] ··· Running timedelta.TimedeltaConstructor.time_from_np_timedelta                                   5.06±0.09μs
[ 43.75%] ··· Running timedelta.TimedeltaConstructor.time_from_string                                          6.52±0.1μs
[ 50.00%] ··· Running timedelta.TimedeltaConstructor.time_from_unit                                            6.66±0.1μs
[ 50.00%] · For pandas commit hash 8acdf801:
[ 50.00%] ·· Building for conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt...
[ 50.00%] ·· Benchmarking conda-py3.6-Cython-matplotlib-numexpr-numpy-openpyxl-pytables-pytest-scipy-sqlalchemy-xlrd-xlsxwriter-xlwt
[ 56.25%] ··· Running timedelta.TimedeltaConstructor.time_from_components                                      15.5±0.3μs
[ 62.50%] ··· Running timedelta.TimedeltaConstructor.time_from_datetime_timedelta                              7.90±0.2μs
[ 68.75%] ··· Running timedelta.TimedeltaConstructor.time_from_int                                             6.11±0.2μs
[ 75.00%] ··· Running timedelta.TimedeltaConstructor.time_from_iso_format                                      25.0±0.7μs
[ 81.25%] ··· Running timedelta.TimedeltaConstructor.time_from_missing                                        2.27±0.06μs
[ 87.50%] ··· Running timedelta.TimedeltaConstructor.time_from_np_timedelta                                    5.04±0.1μs
[ 93.75%] ··· Running timedelta.TimedeltaConstructor.time_from_string                                          7.04±0.2μs
[100.00%] ··· Running timedelta.TimedeltaConstructor.time_from_unit                                            6.51±0.1μs       before           after         ratio
     [8acdf801]       [76475dd8]
-      25.0±0.7μs       12.1±0.4μs     0.48  timedelta.TimedeltaConstructor.time_from_iso_format

SOME BENCHMARKS HAVE CHANGED SIGNIFICANTLY.

[codecov]

Codecov Report

Merging #19191 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #19191   +/-   ##
=======================================
  Coverage   91.52%   91.52%           
=======================================
  Files         147      147           
  Lines       48775    48775           
=======================================
  Hits        44639    44639           
  Misses       4136     4136

Flag	Coverage Δ
#multiple	89.89% <ø> (ø)	⬆️
#single	41.62% <ø> (ø)	⬆️

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[jreback]

lgtm. ping on green (even if the 3.5 conda build fails that's ok, its a travis issue).

[WillAyd]

@jreback all good save the 3.5 build you mentioned

[jreback]

thanks!