Method to_string

code/mathematics/intx.cpp:44–45

        outs << s; } }
    return outs; }
  string to_string() const {
    stringstream ss; ss << *this; return ss.str(); }
  bool operator <(const intx& b) const {
    if (sign != b.sign) return sign < b.sign;
    if (size() != b.size())