Add support for generic-array crate

[Lohann]

In working in a no_std library and to create an ArrayVec where the length is provided by ArrayLength trait, and realized this was not possible. once is not possible to implement the trait Array for third-party crates, the only options are either generic-array add tinyvec as optional dependency and implement the needed trait, or vice-versa.

So this PR implements the trait Array for GenericArray. Combining both I can have trait defined length and the resizable array.

This adds support for generic trait-defined types and length, example:

use generic_array::{ArrayLength, GenericArray};
use tinyvec::{TinyVec, ArrayVec, Array};

pub type GenericArrayVec<T, N> = ArrayVec<GenericArray<T, N>>;
pub type GenericTinyVec<T, N> = TinyVec<GenericArray<T, N>>;

pub trait Config {
    type MaxSize: ArrayLength;
    type Value: Sized + Send + 'static;
}

pub struct Foo<T: Config> {
    pub values: GenericArrayVec<T::Value, T::MaxSize>;
}