ENH: sparse: implement fancy indexing in dok_matrix.__setitem__
TST: sparse: turn on DOK fancy indexing tests
BUG: sparse: fix bugs in DOK setitem for multidim index arrays
ENH: sparse: implement fancy indexing in DOK getitem
ENH: sparse: fast path for DOK scalar setitem
BUG: sparse: fix logic error in DOK getitem

Since i, j can be arbitrary, also for small NNZ one needs to look up
which index in i, j it corresponds to.
BUG: sparse/dok: remove unnecessary broadcasts

_index_to_arrays already broadcasts
BUG: sparse: fix bug in dok_matrix.__setitem__ fast path
ENH: sparse: add fast path for slicing very sparse dok_matrix
ENH: sparse: some performance microtuning in dok_matrix
BUG: sparse: fix dok_matrix empty return
TST: sparse: set numpy random seed, not python random
Merge pull request #3244 from pv/dok-fancy

ENH: sparse: implement fancy indexing for DOK matrices