Prepared Chapter 4 for merge into main.

Added numbering on sections for the table of contents that will follow
in the main file. Removed (commented) the preamble and transferred the
unique parts into main.tex.
TODO: Move all exercises to the end of the chapter instead of having
exercises after each subsection.
Prepared Chapter 5 for merge into main.

Changed a few figure inclusions from \psfig to \includegraphics. Also
added numbering on the sections.
Added preambles from Chapter 4 and 5.
Prepared to merge into main.

Changed some instances of the use of \psfig to \includegraphics.
TODO: Fix some of the tables for aesthetics.
TODO: Move exercises to the end of the chapter, and fix them up so that
the layout looks better.
Added preamble from Chapter 6 (nothing new).