Add recipe for Combinations package

Apparently the Combinations package has been missing a recipe; so
this commit gives it the basic package-building one.
Clean up tex/empirics.tex and tex/simulations.tex recipes

This commit corrects some minor errors in the recipes for the
empirical and simulation tables. It also removes tex/empirics.tex
as a prerequisite for the paper and adds the file to the repo, to
accomodate restrictions on redistributing the file.
Fixup: remove binary file from repository
Remove hardcoded path for latexmk
Correct several errors in build process

This branch corrects a few errors that prevented the Makefile from
finishing.

1. Aspects of the recipes for the simulation and empirical results
   were incorrect or out-of-date and have been fixed.

2. The full dataset was necessary to generate the table of empirical
   results, which is problematic because it can not be distributed.
   I've added the table to the repository and removed it as a
   dependency from the main paper.pdf recipe.

   It can still be generated from scratch through

      make tex/empirics.tex
Add minor comments to stepm code
Fix error in details of Algorithms 2 and 3

Algorithms 2 and 3, as described in the paper, contain errors. They
reverse the order of taking the maximal I in R_{j-1} and taking the
quantile. This problem seems to only be confined to the presentation
and the code and proofs are correct.