Rename undim -> ndim, udtype -> dtype
Move array properties type, dtype, dshape, ndim into nd.*_of functions

a.type -> nd.type_of(a)
a.dtype -> nd.dtype_of(a)
a.dshape -> nd.dshape_of(a)
a.ndim -> nd.ndim_of(a)
Update all the notebooks for the last commit's modifications