Mixture Distribution

Example

```rust extern crate rand; extern crate mix_distribution;

use rand::distributions::{Distribution, Normal}; use mix_distribution::Mix;

let mut rng = rand::thread_rng();

// Mixture of two distributions let mix = { let dists = vec![Normal::new(0.0, 1.0), Normal::new(1.0, 2.0)]; let weights = &[2, 1]; Mix::new(dists, weights) };

mix.sample(&mut rng);

// Mixture of three distributions let mix = { let dists = vec![Normal::new(0.0, 1.0), Normal::new(1.0, 2.0), Normal::new(-1.0, 1.0)]; let weights = &[2, 1, 3]; Mix::new(dists, weights) };

mix.sample(&mut rng); ```