   Returns a BigNumber whose value is the value of this BigNumber modulo
      <code>n</code>, i.e. the integer remainder of dividing this BigNumber by
      <code>n</code>.
    </p>
    <p>
      The result will have the same sign as this BigNumber, and it will match
      that of JavaScript's % operator (within the limits of its precision) and
      BigDecimal's remainder method.
    </p>
    <pre>
1 % 0.9                    // 0.09999999999999998
x = new BigNumber(1)
x.modulo(0.9)              // '0.1'
y