eigen-improvements

eigen:
- no statitically checked dimensions
    - make this a newtype wrapper, a functor,
      so the underlying thing can be anything
- no kronecker product
- express certain properties of a matrix at
  the type level (positive-definite, etc)
- encode things like:
  - 'a `transpose` a' for
  - any real invertible matrix 'a' is positive-definite
  - Every positive definite matrix is invertible and its inverse is also positive definite.
  - Every positive definite matrix is invertible and its inverse is also positive definite.
  - If M is positive semidefinite, then QT M Q is positive semidefinite.
  - note: https://en.wikipedia.org/wiki/Sylvester%27s_criterion
  - note: https://en.wikipedia.org/wiki/Positive-definite_matrix
  - hedgehog generators
  - conversions to JSON and CBOR
  - svd (singular-value decomposition)

there are some things missing from the haskell bindings
also hmatrix has some things that eigen does not support