Enhancement Feature: Simple Complex Number Handling

[amolgorithm]

Noticed that, on this application, taking the square root of -1 resulted in NaN, as JavaScript would naturally evaluate it to.

Although most simple calculator applications do this, perhaps it would be a good idea to extend the calculator's abilities to operations with imaginary & complex numbers, or at least simple operations such as square root of negative numbers and arithmetic with complex numbers.

Of course, simple arithmetic with complex numbers would require an alternative functionality that differentiates them from real numbers, such as an "i" button.

This is effectively and efficiently possible using the math.js library.