Spurious crashes - Switching to enums

Segfaults and stack overflows. I get overflows when running in either
debug or release. Segmentation faults when hooked up to GDB. I think it
may be related to the copying of uninitialized trait objects, but I
don't know.

I've decided the trait-based interface just isn't worth this. I'll
rearrange the materials into an Enum and a big match block.

src/material.rs

@@ -3,11 +3,9 @@ use crate::ray::Ray;
 use crate::hittable::HitRecord;
 use crate::Vec3;
 
-pub struct Material;
-
-pub Scatter {
+pub trait Material {
     fn scatter(
-        ray_in: Ray, rec: HitRecord, attenuation: Vec3, scattered: Ray
+        &self, ray_in: Ray, rec: HitRecord, attenuation: Vec3, scattered: Ray
     ) -> bool;
 }