Typed Array interface using rust-ndarray

[termoshtt]

From #5

[termoshtt]

In #14, we got an interface as ndarray::ArrayViewD<T>. This is enough to enable rust-ndarray functionality for PyArray.

The inverse conversion, e.g. ndarray::Array to PyArray will be implemented as IntoPyArray trait.
It will enable us to convert Vec<T>, &[T], and ndarray::Array to PyArray.

[crackcomm]

Collecting from iterator to PyArray would be very useful:

assert_eq!(arr.iter().map(|x| f(x)).collect::<PyArray>())

[termoshtt]

I add ToPyArray trait at #15:

let arr = (0..10).map(|x| x * x).to_pyarray(gil.python(), &np);

[termoshtt]

Desired functionality has been implemented!