add tests for spsolve
add support for ndarray inputs in spsolve
FIX: spsolve deals with vectors improperly
MAINT: require Cython 0.19

Earlier versions have memory leaks in fused types.
Merge pull request #3096 from pv/cython-req

MAINT: require Cython 0.19
sparse: clean up spsolve code a bit + fix issues with vectors
Merge pull request #3061 from pv/pr-3061

BUG: sparse.linalg: fix bugs in how spsolve deals with "vectors" and ndarray input

This preserves the previous semantics of squeezing (N, 1) input to (N,)
dense output.
DOC: sparse.linalg: clarify gmres maxiter parameter meaning