Implemented toSentance class and chainable method. Also added tests.

I'm am very much open for suggestions on better ways to implement this. I am still learning with Swift.
It is good to create overloaded methods that funnel down to one function that does everything so that if you need to make any changes you make it in one place and all other methods get the benefit. So reuse existing methods when you can and when you can't think of making some helper method that can be used for other purpose and the problem you are trying to solve.