ENH: serialization of categorical to HDF5 (GH7621)
BLD: fix odd usage of cython imports, xref (GH8602)
Merge pull request #8793 from jreback/cat_hdf

ENH: serialization of categorical to HDF5 (GH7621)
DOC: v0.15.2 edits
DOC: v0.15.2 typos