message: Add documentation to BitInt::set_bit
diff: @@ -3271,6 +3271,8 @@ impl BigInt {
  }
  }
  + /// Sets or clears the bit in the given position,
  + /// uses the two's complement for negative numbers
  pub fn set_bit(&mut self, bit: u64, value: bool) {
  match self.sign {
  Sign::Plus => self.data.set_bit(bit, value),
  