More matrix ops native functions

[Henrik Moller]

    Added eigenvectors/eigenvalues, vector internal angle
      calculation, and identity matrix generation.
      
      For those of you who might be into graphics, openGL rotation,
      instead of using decomposed Euler angles or Tait–Bryan angles, use
      a scalar angle and a rotation axis.  That's why mtx supports the
      mtx['a'] "angle" function and the mtx['c'] cross product
      function--the cross product of two vectors is the rotation axis
      around which you rotate to get from one vector to the other. 
      (This kind of rotation specification makes it easy to do smooth
      rotations in animation.)