#108 interface for zheev in lapack

[Robert Dodier]

Copied from bug report #2634 by Dominik Wondrousch: "Could you implement an interface to zheev as well ? This is the same thing for complex hermitian matrices. Although one can solve the same problems using zgeev, there is a significant difference: zgeev does NOT orthonormalize eigenvectors for degenerate eigenvalues, zheev does because herimitian eigenvectors are supposed to be orthonormal. I know, there is gramschmidt, but using the numerical results of zgeev, this turns out to be numerically instable."

[Dominik Wondrousch]

Thanks for splitting the topics.

[Raymond Toy]

zheev support has been added