DOC: add docstring
WIP: finish on #2856
DOC: fix typo
PERF: fixed int64 indexing perf issue when conversion to int64
Merge pull request #3327 from jreback/index_perf

PERF: fixed int64 indexing perf issue when conversion to int64
PERF/CLN: infer Period in infer_dtype, later index inference is faster
Merge pull request #3329 from jreback/period_perf

PERF/CLN: infer Period in infer_dtype, later index inference is faster

doesn't completely fix the problem (though though could just be noise), but helps in lots of other cases....
BLD: Cache 2to3 Artifacts
BLD: refine files filter in Cython build cache code
BLD: travis network cache