Animation system

[LetsMelon]

Ideas:

• start_frame and end_frame, TODO make frame a type
• curve (trait?)
• called every time before a new png is rendered

struct Animation {
  start_frame: usize,
  end_frame: usize,
  curve: &'a Curve,
}

fn main() {
  // 60fps, 2s
  let animation = Animation {
     start_frame: 60,
     end_frame: 180,
     curve: todo!(),
  };
}

[LetsMelon]

I think the current system from animation works fine enough for version 0.1. In the future I want to have the animation on the "path" and not on the renderer.