Use Default::default instead of new in traits

[morenol]

I'm submitting a

• [x] improvement.

Current Behaviour:

Currently, traits in https://github.com/smartcorelib/smartcore/blob/development/src/api.rs#L24 requires implementation of fn new() -> Self;, I think that instead we should rely on Default::default,

Do you want to work on this issue?

Yes

Any thoughts?

[Mec-iS]

I had to implement the new() method as it looked like the best way of passing the estimators to cross_validate and cross_validate_predict. If you find a better way would be happy to go for it.

[morenol]

gotcha, I think that we can use generics to define the type that we need to use instead of passing a blank parameter that is not used