fix tmy3 leapyear in February handling, coerce_year raises exception (pvlib#866)

* create test for GH865

* checks if there is a 2/29 in the parsed output
* checks if can use coerce year

* check it's really greensboro

* also check that year is actually coerced

* check if the TMY Feb contains a leapyear

* then change 2/29 to 3/1
* add sanity check, indices should increase monotonically, by 1hr,
  except perhaps the last hour, which might be the previous year.
* add FIXME for coerce_year, should last hour be Jan1 of the next year?

* add data file, update what's new

* stickler space around operator in test

* move warning after notes

* oops, copy and paste error

* remove redundant Greensboro meta check

* use improved snippet from Kevin Anderson

* remove dateutil import
* remove _parsedate

* use 'h' unit string in pd.to_timedelta for min req pandas-0.18.1

* fix first and last hour issue are 1AM and midnite

* elaborate on warning regarding definition of TMY and possibly
  unexpected behavior when coercing the year
* add more comments
* use mod instead of subtracting hour to change midnite from 24 to zero
* shift all midnite rows one day forward
* check for leapday (2/29) and shift to March 1st
* add copious comments and a note that if pandas is updated to 0.24
  then we can use the `array` property to detect leapday
* add test to confirm that TMY3 1st hour is 1AM and last hour is midnite

* remove unneeded numpy import in iotools/tmy

* update what's new to explain that tmy3 dataframe now has original Date
  and Time columns used to parse the indices

* more explicit test for 2/29/1996 in tmy3

* wait to set index to avoid error in py35-min

* ValueError: cannot reindex from a duplicate axis

* try pandas datetime instead of index

* no need to convert data_ymd to datetime

* it ALREADY IS! ha ha ha

Author: mikofski

docs/sphinx/source/whatsnew/v0.7.2.rst

@@ -3,6 +3,17 @@
 v0.7.2 (Month day, year)
 -------------------------
 
+Enhancements
+~~~~~~~~~~~~
+* TMY3 dataframe returned by :py:func:`~pvlib.iotools.read_tmy3` now contains
+  the original ``Date (MM/DD/YYYY)`` and ``Time (HH:MM)`` columns that the
+  indices were parsed from (:pull:`866`)
+
+Bug fixes
+~~~~~~~~~
+* Fix :py:func:`~pvlib.iotools.read_tmy3` parsing when February contains
+  a leap year (:pull:`866`)
+
 Documentation
 ~~~~~~~~~~~~~
 * Add NumFOCUS affiliation to Sphinx documentation :pull:`862`