The diffusion tensor data structure now returns the matrices 'tensor' and 'tensor_diag'.
For spherical, spheroidal, and ellipsoidal diffusion, the diffusion tensor data structure attributes
'tensor' and 'tensor_diag' now exist. These return the diffusion tensor in the form of a matrix.
The object 'tensor_diag' returns the diffusion tensor defined within the diffusion frame. The
object 'tensor' return the diffusion tensor defined within the structural frame.
