Inspiration for implementing the Gaussian process methods came from
the work of Carl Rasmussen and Chris Williams.  I also benefitted
from looking at Carl Rasmussen's implementation.

The sampling method for top-level hyperparameters using adaptive
rejection sampling, and the features allowing cpu time to be stored,
displayed, and used to control the number of iterations, are also
based on work by Carl Edward Rasmussen.

Thanks also to David MacKay and Chris Williams for testing the
programs on their machines, and for comments on the documentation.