`matmul` on multidimensional arrays

[mtar]

Description Matmul does not work on distributed arrays with more than 2 dimensions.

To Reproduce Steps to reproduce the behavior:

1. Which module/class/function is affected? linalg.matmul
2. What are the circumstances under which the bug appears? dim > 2
3. What is the exact error message / erroneous behavior? depends on split value ValueError: If the last dimension of a (4) is not the same size as the second-to-last dimension of b. (4) ZeroDivisionError: integer division or modulo by zero mpi4py.MPI.Exception: MPI_ERR_TRUNCATE: message truncated NotImplementedError: splits > 1 not implemented

Expected behavior Matrix multiplication of the last two dimensions

Version Info master