Returns a BigNumber whose value is the value of this BigNumber shifted by n places.

The shift is of the decimal point, i.e. of powers of ten, and is to the left if n is negative or to the right if n is positive.

The return value is always exact and unrounded.

Throws if n is invalid.

x = new BigNumber(1.23)
x.shiftedBy(3)                      // '1230'
x.shiftedBy(-3)                     // '0.00123'