usage: nvol = gquadnd (fun,lowerlim,upperlim,nquad);
n -- number of dimensions to integrate
nvol -- value of the n-dimensional integral
fun -- fun(x) (function to be integrated) in this case treat
all the different values of x as different variables
as opposed to different instances of the same variable
x -- n length vector of coordinates
lowerlim-- n length vector of lower limits of integration
upperlim-- n length vector of upper limits of integration
nquad -- n length vector of number of gauss points
in each integration
