Impl Demand, Returns Plan classes and scenarios
Updates Purchasing Plan cost calculations
Updates SS_Plan to consider POD as safety stock
Adds common spec file and scenario what-ifs
Updates backlog in questions.txt
Updates data files
Updates cost calculations to reflect print choices
Update questions and backlog
Updates questions.txt with another question
7/13/14 lesson
Updates technology_types
Shortens file names in determine_plan
Partially updates cost function
Simplifies calc_costs with list comprehensions
Eliminates globals in calc_cost method
Merge branch 'dev'
Updates with outline for ROP changes
Implements partial logic for cumulative sd in ROP.
Updates ROP calculations
Corrects logic in calc_leadtime_sd

Indexes in i, j and horizon were off