I made a separate filterpy.stats module becuase it made
little sense to import filterpy.common for stats
functions. This required a lot of changes in the notebooks
and supporting code.
I made a lot of changes so that each chapter makes clear that
they are all implementing the same basic bayesian algorithm.
This required a lot of editting, and it doesn't make sense to
try to do that atomically, hence this huge check in.
I made a lot of edits, and haven't copy editted anything. i'm
sure I introduced a lot of problems and discontinuities.
Added better explanation of P = FPF' + Q.
Moved conversion of multivariate equations to univariate eqs. to the
math chapter.
Moved the walkthrough of KalmanFilter to an appendix.
My charts were mixing position vs time, which was pretty confusing.
I changed it to position vs velocity, and demonstrated how multipying
the covariances lead to a much better result.
Several changes and clarifications. Added chart showing 2d distribution
of points for multivariate gaussian. Improved some discussions. Fixed
some typos.
