Write a function defined as: def GaussIntegration(fcn, a, b, n=4): Purpose: use the Gauss Integration method to estimate the integral of fcn(x), between the limits of a and b.
fcn: the function we want to integrate
a and b: the lower and upper limits of integration
n: The number of integration points used. The only acceptable values are 2, 3 and 4. If a value other that 2, 3 or 4 is passed, use n = 4.
return value: the estimate of the integral.