WIP: Index no longer an ndarray sub-class (GH5080)

CLN: add searchsorted to core/base (GH6712, GH7447, GH6469)

fixup tests in test_timeseries for reverse ndarray/datetimeindex comparisons

fix algos / multi-index repeat (essentially this is a bug-fix)

ENH: add NumericIndex and operators, related (GH7439)
DOC: indexing/v0.15.0 docs