Release 0.1.1

Added

• Add Scene abstraction with pluggable Sky trait.
• Allow iterators of Vec3 to be summed with .sum().
• Add animated progress bar with indicatif.
• Add Debug + Send + Sync bounds to Hittable, Material, and Sky traits.

Changed

• Extract ray tracer into separate render() function, which produces a sequence of pixel color values.
• Integrate with rayon to calculate each scanline, row pixel, and component pixel color samples in parallel.
• Replace Box<dyn Material> trait object with generic type parameter in Sphere.

Fixed

• Correct the Vec preallocation amount in random_scene() to 22 ⋅ 22 + 4.