Data-Science Code Review

Joe,
I forked level_up_exercises and imported solutions that I had been placing in a different project. Going forward I will use this fork to submit pull-requests.

Zamir
extract lines 10-19 (and all other instances of this pattern within this spec) into their own test on the `<<` method, as separate cases (along the lines of: `it reassigns @value when the argument greater than the previous @value`, `it does not reassign @value when the argument is less than the previous @value`, etc)