Add gradle build environment
Remove java files in old location
Add main class to jar manifest
Change RouletteWheelSampler to take Map<T, Double> to reduce needed code.  Update references.
Add unit test for RouletteWheelSampler
Refactor MarkovModel into MarkovModel and MarkovProcess.  Add unit tests.  Fix bug where first state was being skipped.
Move MarkovModel tests to the appropriate package
Remove pets, transaction triggers from Customer
Change StoreGenerator's instantiation of RouletteWheelSampler to use create()
remove unneeded imports from Customer
Remove unneeded imports
Added unit test for NameReader
Use immutable data structures in ZipcodeRecord / ZipcodeReader
Add unit test for ZipcodeReader
Move Store, Customer, Transaction into new package.  Add getters and constructor for Transaction
Removed unneeded samplers.  Added tests for others
Added ProductsReader with test
Add unit tests for StoreGenerator and zipcode samplers
Moved ProductCategory into inputs
Added getLocation() to Customer