PUBDEV-8911: Added M-spline implementation to docs (#6425)
PUBDEV-8911: Added M-spline implementation to docs (#6425)

* PUBDEV-8911: m-spline first draft

* PUBDEV-8911: Added example

* PUBDEV-8911: requested updated

num_knots note; penaltymat updates
h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3,h2oai/h2o-3