Add multi dimensional array support to clad::array and clad::array_ref

[sudo-panda]

Currently clad::array and clad::array_ref only supports single dimensional arrays. If this feature is added clad will be able to differentiate multidimensional arrays. Possible design decisions include:

• Storage: Multidimensional or Single dimensional
• Interface: Do we require reduced dimensionality indexing (not sure what the term is) eg. 2 dimensional indexing in a 3 dimensional array arr[2][1] instead of arr[2][1][0].

[vgvassilev]

@vaithak, now that we added clad::matrix would that be sufficient to move forward with this issue?