* Fix an annoying typo/bug in coenocline2d which was using the expanded gradient locations on y for the locations on x
 * Fix the bivariate Poisson example to expand.grid the gradient locations
 * Add a two species bivariate Gaussian example with perspective plots - helps track down the typo/bug above
 * Added a perspective plot to the Poisson bivariate Gaussian
 * Added headers to make the various examples in ?coenocline stand out