Added a voigt routine and check for symmetry to utils
Modified the holzapfel tangent stiffness.

It's still incorrect, though.  We need symmetry, but F*Ai is not
symmetric.
Add antisymmetrizer to utils
Fixed holzapfel_D, now appears to work
Added a more realistic cost function (field5) plus misc
Compute structure tensors from fiber directions
Added some parameterizations for strain