function RC4(seed) {
    this.s = new Array(256);
    this.i = 0;
    this.j = 0;
    for (let i = 0; i < 256; i++) {
        this.s[i] = i;
    }
    if (seed) {
        this.mix(seed);
    }
}
@param {String} seed A string to seed the generator.
@constructor