REF: working toward #1150, broke apart Cython module into generated _algos extension
REF: have got things mostly working for #1150
BUG: more bug fixes, have to fix intraday frequencies still
BUG: more intraday unit fixes
BUG: test suite passes, though negative ordinals broken
BUG: weekly and business daily unit support #1150
REF: remove period multipliers, close #1199
ENH: move _ensure_{dtype} functions to Cython for speedup, close #1221
DOC: doc fixes
ENH: handle dict return values and vbench, close #823
ENH: add is_full method to PeriodIndex close #1114
Remove dependencies on details of experimental numpy datetime64 ABI

Pandas was using some of the enums and structures exposed by its headers.
By creating its own local copies of these, it is possible to allow the
numpy ABI to be improved while in its experimental state.
Use datetime64 with a 'us' unit explicitly, for 1.6 and 1.7 compatibility
Use an explicit unit for the 1.7 datetime64 scalar constructor
Use assert_equal instead of assert, to see the actual values
Microseconds (us) not milliseconds (ms)
TST: use NaT value
ENH: #1020 implementation. needs tests and adding to API
ENH: add docs and add match function to API, close #502
ENH: add Cython nth/last functions, vbenchmarks. close #1043