Add area light material

src/material.c

@@ -68,3 +68,16 @@ bool scatter_dielectric(
 
 	return true;
 }
+
+bool scatter_area_light(
+    material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
+    vec3_t *atten_out)
+{
+	(void)hit;
+	(void)rng;
+	(void)ray;
+
+	*atten_out
+	    = vec3_scale(params.area_light.colour, params.area_light.luminosity);
+	return false;
+}