Bivariate Normal Distribution Plot

A quick description (with pictures) is here:

http://dobor.blogspot.com/2014/01/plotting-bivariate-gaussian-density.html

Plot contours and the surface of the bivariate normal distribution. Change the parameters and see how the distribution changes: change the entries in the covariance matrix and see how the shape of the distribution is altered; change the the entries in the mean vector only and move the distribution in space without altering its shape.