[Refactor] Improve type safety with std::complex

[kluophysics]

Motivation

Recent trial of including f2c.h leads to conflicts with the complex type defined there typedef struct { real r, i; } complex;.

What's changed?

• All complex<double> and complex<float> occurrances including tests have been replaced by std::complex<double> and std::complex<float>
• Arguments with complex<T> without a space separation has been modified to have it. Example: double,complex<double> is changed to double, std::complex<double>.

Discussions

I had thought about using trick like

template <typename T>
using complex=std::complex<T>;

to do it, but it still has the same problem. So I stick to this more cumbersome.

[mohanchen]

Excellent work! Thank you so much for these contributions !! @kluophysics