code: function(up, down, symbol, weight) {
      this.up = up; // next node up the tree
      this.down = down; // pair of down nodes
      this.symbol = symbol;       // node symbol value
      this.weight = weight;       // node weight
  }
docs: huff_init(alphabet_size, potential symbols used) huff_encode(next_symbol) next_symbol = huff_decode() huff_scale(by_bits) -- scale weights and re-balance tree