* Consider the performance of using column-major matrices everywhere, instead
  of just where LAPACK is used (LAPACK uses column-major order).

* Implement rot_rate_mat_forward and derivatives. I think the equations were
  in Fossen.

* Create some functions for 3x3 matrix multiplication, matrix-vector 
  multiplication etc where the matrices are stored in double arrays. These
  could be used in frequently called functions such as the pose composition
  functions while producing cleaner code than what is in there currently.

