implement nonzero
Merge commit 'b5b0f1abb077a6a42d3a529e2fa2a61b0dce75cd' into sane
update nonzero definition for scalars
Merge commit '11a43017e2b99c7fb65bb4c1d731d7e8eb223afd' into sane
revert to ischeme as points, weights tuple
restore unit tests