Reorganize linear regression material

This commit moves around some of the linear regression material;
- Asymptotic statistical properties are moved to the asymptotics document
- Algebraic properties and multiple testing are moved to the linear
  regression document
- Move material about normal r.v.s and quadratif forms to the probability
  introduction
- Some edits are made to the finite sample inference and estimtion documents.

reorg
Reorganize finite-sample material

This commit moves the finite sample material around and prettys up its
source code.
Move version number back to year field of bibtex entry

This commit moves the project's version number back into the year field for the
provided bibtex record.  It should be in the text when cited.
Revise and rewrite introductory probability material on moments and densities

This commit cleans up some of the source code, moves around probability material,
and fleshes out the text covering moments and specific distributions.