Replace unicode copyright symbol

We're going to move away from unicode to try to make the editing as easy
as possible for other contributors.  This commit starts that process
by replacing the unicode copyright symbol with ASCII or TeX versions.
Make single tex file for entire book

This commit moves the individual parts into a master tex file,
'core_econometrics.tex,' that compiles to a single pdf for the
entire book.  This should make it easier to disseminate the
book and make it easier for contributors to figure out the
internal architecture.
Convert files from xelatex to pdflatex

This commit is a large conversion that aims to make the files
easier for potential contributors to work on.  It converts
the files from using the XeLaTeX engine to build pdfs from
unicode source files to the pdfLaTeX engine and ASCII source
files.