[Enhancement] Add the possibility to get the factorial of a number

[lpeyr]

Enhancement

Add the possibility to get the factorial of a number.

Other informations

Add a method in Maths.

Implementation:

public static int Factorial(int n)
{
	if (n == 1 || n == 0) return 1;
	int r = 1;
	
	for (int i = 1; i <= (n < 0 ? 0 - n : n); i++)
	{
		r *= i;
	}
	
	return (n < 0 ? 0 - r : r);
}