Basic Implementation - added categories as an extension

Implemented hangman and added an interface, also created some cucumber tests, capybara tests and rspec tests. 
Rather than creating an instance of Answer in the initializer I would always prefer to do it in a separate method. Or when you can it's always better to create the instance of answer somewhere else and then pass it into Game directly

```
def answer
  @answer ||= Answer.new(@filename)
end 
```