Complex numbers in polar form

[Pol Welter]

We now have complex numbers. That's a win.

To make it even better we now require a way to display them in polar form. Possibly make it dependent on angle setting by explicitly including degree in the result.

polar((1+1j)/sqrt(2)) = 1 exp(j *  45 degree)

Similarly, we need the functions rect(z) and phase(z). Fortunately abs is available already.

[Helder Correia]

See pull request #68.