Support complex number

[yancyn]

Do you have any plan to add support variable as complex number, i? Since .NET 4.0 or .NET 4.5, Microsoft start introduce System.Numerics.Complex, and Imaginary number.

This is very useful especially in composing math expression in electronic engineering computing. Or you can give me some tips maybe I can try to fork your repo and extend myself. Or should I go for NCalc for more easier implementation? (As I know, NCalc also not support yet).