Move R code to separate files

This commit moves the embedded R code outside the document
and then uses the fancyvrb package to display it inline. The
book no longer uses knitr and this is hopefully a more
approachable setup.
Convert bootstrap code from R to Julia

This commit translates the bootstrap code from R to
Julia. I'm going to change all of the code to Julia
eventually.
Convert model selection code to Julia

This commit translates the code for the model selection chapter
to Julia from R.