Set and correct tex-master variable

Each of the files sets a master file for emacs's AucTeX mode.  This
variable was missing in many of the subfiles, or set incorrectly.
Simplify latexmk call in Makefile slightly

This commit changes the latexmk flags to use xelatex specifically.
Add bibliographic references and tweak style

Starts a local bibtex database with a few textbook entries and changes
the reference style to author-year with rounded parentheses.
Add homework problems to probability overview

* Adds a first draft of some homework problems from the classes I've taught,
  both theoretical and computational problems.
* Updates the main text and the makefile to include a bibliography; the
  homework refers to a few other textbooks.
Add homework problems for point estimation material

I've added a few questions from my course notes for Econ 671 at Iowa
State.
Add homework problems for Inference material
Add homework problems for linear regression notes

I've added a few homework problems from my 671 course notes.
Add table of set theory results

A table of set theory results was typically given out as a class handout;
it's been moved into the axiomatic probability introduction.
Patch: add linear regression document to makefile
Merge branch 'patch_makefile' into dev

The linear regression document had been omitted from the Makefile; this
patch puts it in.
Patch: correct LaTeX error in Linear Regression homework

The linear regression problem set uses an undefined macro, \sd.  This patch
removes that macro and just uses 'sd'.  It's not a fantastic workaround,
but the LaTeX code in that part of the document needs to be heavily
refactored anyway.
Merge branch 'patch_linearregression_problems' into dev

The linear regression problem set uses an undefined macro, \sd.  This patch
removes that macro and just uses 'sd'.  It's not a fantastic workaround,
but the LaTeX code in that part of the document needs to be heavily
refactored anyway.
Remove version number from README file

This is a change in the way I'm storing things; I want the version info
to be generated on the fly and not contained in the repo, except in the
NEWS.md file.
Remove version info from repository

This patch uses git shell commands to set the date and version in each
LaTeX file on-the-fly.  It introduces the 'ver' target for the makefile,
which writes the current date and version to an unversioned file
'VERSION.tex' (the name choice might not be the most intuitive...) and
the LaTeX file imports it to set the date and version.
Remove section numbering from ADDENDUM of License

This change makes the license stylistically in line with the FSF's
original copy.
Move licensing documentation to a standalone file

To save on paper and space, I've moved the GNU FDL to a separate pdf and
taken it out of the individual documents.  This seems consistent with
Section 6 of the license (Collections of Documents), since this entire
repository is best viewed as a single collection.  I've commented out the
LaTeX code to include the license in the individual pdfs, so if anyone
wants to distribute any of them on their own it should be very easy to
reintroduce the text and comply with the FDL.
Merge patch correcting Makefile dependencies
Release version 0.1.4

* Add homework problems to each document
* Add table of set theory results that was a former handout
* Split off linear regression materials as a separate document
* Move licensing information to a standalone handout
* Split off versioning information from repo and generate document
  dates on-the-fly (type make ver; make -j).