Tomohiro Ichinose

Improve generics usability for `Array<T>`

7

I encountered difficulty when writing generic functions using `Array` e.g. ```rust fn test_basic_op(a: &af::Array) where // T: af::Fromf64 + af::HasAfEnum + ??? { println!("Element-wise arithmetic"); let b = af::add(&af::sin(a), &T::fromf64(1.5f64),...