Implement Correlated Multi-Jittered Sampling

[CaffeineViking]

In order for us to more easily compare with ground-truth once we've implemented e.g. "Phone-Wire AA", we should multi-sample each raytraced pixel by using a unbiased sampling pattern, such as CMJ as in the paper:

vec2 cmj(int s, int m, int n, int p) {
    int sx = permute(s % m, m, p * 0xa511e9b3);
    int sy = permute(s / m, n, p * 0x63d83595);
    float jx = randfloat(s, p * 0xa399d265);
    float jy = randfloat(s, p * 0x711ad6a5);
    vec2 r = vec2((s % m + (sy + jx) / n) / m,
                  (s / m + (sx + jy) / m) / n);
    return r;
}

[CaffeineViking]

Done!