interoperation with scipy.sparse

[ev-br]

Just wait for __numpy_ufunc__ or is there something one can sensibly do (converting to csr and handling that?)

[ev-br]

One option: if it has a tocsr() attribute, use it and convert the result from csr to map_array.

[ev-br]

#29 implements a partial solution: check for a .tocoo attribute and try converting the result to a MapArray. This mostly works, with two weird corner cases:

• multiplication with csr_matrix on the left. This fails because it checks dimension for matmul before giving up. This way, map*csr is always elementwise, but csr*map fails with a ValueError for non-square matrices. Maybe just prohibit multiplication altogether?
• comparions with csr on the left. map > csr is OK, but csr > map isn't.