Returns true if the value of this BigNumber is greater than the value of n, otherwise returns false.

0.1 > (0.3 - 0.2)                             // true
x = new BigNumber(0.1)
x.isGreaterThan(BigNumber(0.3).minus(0.2))    // false
BigNumber(0).isGreaterThan(x)                 // false
BigNumber(11, 3).isGreaterThan(11.1, 2)       // true