added hemispherical scattering, switched to ppm version 6

src/material.rs

@@ -0,0 +1,13 @@
+use crate::hittable::HitRecord;
+use crate::ray::Ray;
+use crate::rtweekend::*;
+use crate::hittable_list::*;
+use crate::vec3::Color;
+
+pub struct Material {
+
+}
+
+trait Scatter {
+    fn scatter(r_in: &Ray, rec: HitRecord, attenuation: &Color, scattered: &Ray) -> bool;
+}