RSTSR dtype Traits

This trait tries to resolve some function clashes in crate num. For example:

• abs function may have different behaviors for Signed and ComplexFloat,
• max and min function is defined by f64, trait Ord (where max or min is defined in standard library) is not implemented for f64.

For those functions, it is more proper to define traits for each function specifically.

We only implements several types in standard library, or complex values. More types (from other crates) will be added in future or by issue request.