Rewrite brief introduction to linear regression material

This release is a rewrite of the very short introduction for part 4,
the linear regression material.  It is still very short, but now it's
not an outline.
Update 'xelatex' reference to 'latex' in README
Rewrite latex inclusion of generated files

This commit adds new commands to give default values of the
citation information, version number, and figures.  These
files are generated by make and may not be present if someone
opens core_econometrics.tex and starts hacking; now that will
work, but there will be placeholders in the generated pdf.

There's a safety check, though, so if the 'final' option is
set in the documentclass, LaTeX throws an error if files are
missing."
Convert Sweave code to LaTeX listings

This commit switches from Sweave to using the listings package
with basic R code.
Set seed for bootstrap application
Merge branch 'recode-bootstrap'
Tweak size of bootstrap figures

This commit makes the bootstrap figures narrower so they fit on
the page.
Switch to literate-style coding for bootstrap

This commit switches the code to be embedded in the LaTeX source
and then extracts it with knitr.
Add files generated for bootstrap to repo

Not sure that this is the best way to go, but this commit embeds
the figures and macros for the bootstrap in the repository.  This
should make it easier for people unfamiliar with R and the linux
command line to contribute to the rest of the book.
Add citations for R and knitr
Update documentation
Merge branch 'literate-knitr'

Conflicts:
	asymptotics/bootstrap_fig1.R
	asymptotics/bootstrap_fig2.R
Update clean and burn targets

Since there are some generated files in the repo, I've
taken them out of 'make clean' and 'make burn'.
Update figures for new widths (fixup)

This commit adds figures with the correct widths to the repo.  Commit
c9e8cc6 updated the code, but we forgot to add the new plots.
Make several cosmetic changes to the document

- Reverts fonts to Computer Modern (default): the tufte-latex
  serif/unserif/mono combinations are horrible together.  I'd
  like to have something better than CM, but don't want to spend
  a lot of time thinking about it now.  This issue has bothered
  me more now that there's a fair bit of embedded R code.

- Removes "list of figures" etc.  They can go back in later, but
  they too need some more thought.

- Change back to the tufte-handout class to save some paper and
  have a more natural pdf reading experience.

- Remove the 'literate' style typesetting of R code.  It's pretty,
  but it will probably just confuse students and potential
  contributors.
Fixup: correct section heading for 'issues in modeling'
Remove 'localmod.tex' from repo

Removing 'localmod.tex' from the repository will make it easier to
modify locally.
Merge branch 'master' into add-refs

Conflicts:
	asymptotics/problems.tex
	finitesample/problems.tex
	probability/problems.tex
	regression/problems.tex
	tex/references.bib
Add local modifications file to ignore list

Forgot to add local modifications file to ignore list last commit.
Merge branch 'master' into add-refs