Merge branch 'dev'
Merge branch 'dev', version 0.1.1

* Moves preamble material to a shared repository and streamlines the code
* Fixes some issues in the appearance of the main texts
* Changes to a more informative title and author
Hotfix release 0.1.2 to correct a bug in makefile

The makefile wasn't handling automatic directory detection correctly.
This release puts the pdfs into a variable and used the wildcard function
explicitly in a double colon rule, and that should hopefully fix it.
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.