Add percent complete readout in terminal

src/camera.rs

@@ -58,6 +58,14 @@ impl PerspectiveCamera {
         dir: Vec3::new(sensor_x, sensor_y, 1.0).normalize(),
       }
   }
+
+  pub fn percent_complete(&self, row: u32) -> f64 {
+      let float_row = row as f64;
+      let float_scene_height = self.scene_height as f64;
+      let float_scene_width = self.scene_width as f64;
+
+      ((float_row * float_scene_width) / (float_scene_width * float_scene_height)) * 100.0
+  }
 }
 
 impl RaySource for PerspectiveCamera {