Change types of complex numbers to c32 and c64

[certik]

It seems much more natural to me, and consistent with quite a few codes and libraries:

• https://arrayfire.org/docs/gettingstarted.htm
• https://michaelhatherly.github.io/NumericSuffixes.jl/stable/
• rename Complex{32,64,128} to ComplexF{16,32,64} JuliaLang/julia#24647
• https://docs.rs/cauchy/latest/cauchy/type.c64.html

Essentially, it means the complex number is composed of the 32 or 64 bit float. One says double precision complex number, and double precision is 64 bit, so it's 64 bit complex number, c64 (yes, it is represented by 128bits).