fight the t distribution

lose and slinky back to my castle
Switch back to using kernel density estimates (upon giving up the t-distribution)
Merge

I used a merge branch (for safety) and git merge --no-commit; git add -p; to cherry pick diffs; this fixes the bad merge resolution but keeps the changes made to the docs
TODOs
Split MultivariableRegression into implementation, tests, and test runner like the other code
Started on Example, made some changes to report and fixed Mahalbolos (no clue how it's actually written) bug by changing to literal matrix algebra.
forgot -a on commit before
Merge https://github.com/kousu/stat440

Conflicts:
	R/MultivariableRegression.R
	R/test.speed.main.R