Change hamming tests to test against instance methods

The hamming tests were testing against class methods yet the Getting Started document refers to hamming as an object and the solution given for the first test is an instance method. Based on the evidence of the getting started document and exercise being the first I have presumed that the tests should of been against an instance method not a class method. I have corrected the tests to initialise a hamming object before calling the methods.

Fixes #52