pep8 cleanup of test_linprog.py
Minor documentation issues fixed.
Thanks to a suite of helpful test cases I was able to pin down a bug involving incorrect "tie breakers" when selecting pivot elements. (https://gist.github.com/denis-bz/8647461)
Refactored _solve_simplex and added _pivot_col and _pivot_row functions to simplify things a bit.
Unit tests all pass, and those cases at the above gist finish on a valid vertex of the simplex.