Added Matérn and linear regression kernels. Getting closer to Trautman's
implementation.
Created a parametric gaussian process that allows separate kernels for x and y.
Added Trautman's hyperparameters and reorganized the plots.
Created a bunch of examples of the current kernel combination.
Adjust the amount we add to the diagonal to ensure positive definiteness.
Compulsively forcing UTF-8 encoding so I can use the accented e in Matérn.
Generated some more demos at a larger scale and they look much more sensible, though still possibly weird.