Revert "Temporarily remove linear-regression prediction material"

This reverts commit f51640f4e4b064782632c9e63682d93c5f7d89c6.
I probably should not remove material from old versions w/out
extremely good reasons, even if they need to be heavily revised.
Revert "Temporarily remove Bayesian material"

This reverts commit 2460007544aed068d48876866b31671ff2834b56.
Ditto.  Shouldn't remove old material unless it's permanent.