add comparisons operator to the Period object and fixes issue 2781
move the Period tests in test_period.py and add assertRaises tests for comparisons
use a function factory for comparisons of Period objects
BUG: guard against i < -len(series) in get_value_box fast code path. re: #3168
DOC: release notes
ENH: replace some usages of DataFrame to more generic self._constructor. #2865
ENH: better error message when discretization might create an ambiguity. close #1978
BUG: fix parser case using Timestamp as a date parser. close #2932
fix issue 2926
add tests for issue 2926
DOC: release notes
Merge remote-tracking branch 'Moisan/period_bug'

* Moisan/period_bug:
  use a function factory for comparisons of Period objects
  move the Period tests in test_period.py and add assertRaises tests for comparisons
  add comparisons operator to the Period object and fixes issue 2781
DOC: release notes
BUG: fix bug when concatenating series with axis=1 and they have the same name. close #2797
CLN: refactor core/index and tseries/index,period to have their formats and to_native_types be consistent
     in naming / operation
ENH: add support for Period formatting (as a native type)
TST: add period support to makeCustomDataFrame for testing purposes
BUG/TST: format multi-index nan correctly