Some std features of external crates aren't re-exported

[alvinhochun]

Some functions, for example Complex::to_polar, are listed in the docs, but since they are under the std feature of external crates (e.g. num-complex) and not re-exported by nalgebra these methods can't actually be used.

[sebcrozet]

Hi! I’m not sure I understand the problem. Does your create depend on num-complex too? In that case enabling its std feature should work.

[sebcrozet]

Ah, nevermind, you are referring to the Complex type reexported by nalgebra. Yeah, we should transitively enable num-complex/std.