Missing basic Matrix Operations

[Xyhlon]

In the commit history a trace method used to exits, why doesn't it exist anymore. 215ccdc
I would be great to support this because the following code is a bit unergonomic.

        let trace_val = exp_neg_beta_H.trace();

instead of:

        let trace_val = exp_neg_beta_H.to_diag().reduce(C64::new(0.0,0.0), |acc, elem| acc+elem);

Furthermore other Matrix Operations like:
Hermitian Conjugation

exp_neg_beta_H.t().fmap(|x| x.conj())
// vs
exp_neg_beta_H.h()

real and imaginary part operators.

Support for rusts built-in iter trait.

Matrix Exponentials