Provides functions to generate response-surface designs,
fit first- and second-order response-surface models,
make surface plots, obtain the path of steepest ascent,
and do canonical analysis. A good reference on these methods
is Chapter 10 of Wu, C-F J and Hamada, M (2009)
"Experiments: Planning, Analysis, and Parameter Design Optimization"
ISBN 978-0-471-69946-0. An early version of the package is
documented in Journal of Statistical Software