Data science 20141007 rc

Revisions based on previous Pull Request: https://github.com/jmmastey/level_up_exercises/pull/138

-break out `CONFIDENCE_LEVEL` and `PROBABILITY_THRESHOLD` into constants
-print out the clear winner or warning that there is no clear winner
-changed Dataset tests to check three sample files; winner a, winner b, no clear winner
-removed unused `total_sample_size` method
this main.rb file is more than a dump runner file. It seems to have some SplitTest specific logic. It may be a good idea to had a main.rb file (with no class def) just run a more appropriately named class (e.g. SplitTest) with helper methods to calculate and output. I really like how you accomplish a lot with simple files. However, I think this scenario has a tad bit too much logic in the 'main' file (enough to create an appropriately named class). You can actually remove main all together when you have a SplitTest.rb where after the class info you put the test runner stuff so you can just `ruby split_test.rb`