BUG: fix multi-column sort that includes Categoricals (GH7848)
CLN: refactor _lexsort_indexer to use Categoricals
BUG: Categorical concat should preserve levels (GH7864)
Merge pull request #7850 from jreback/cat_sort

BUG: fix multi-column sort that includes Categoricals / concat (GH7848/GH7864)
WIP: Index no longer an ndarray sub-class (GH5080)
fix _simple_new (maybe should be combined across indexes though)
CLN: add searchsorted to core/base (GH6712, GH7447, GH6469)
period almost fixed completely
fixed issue in copy, not calling _simple_new
fixed up test_timeseries.py a bit