PLEASE CODE REVIEW. This is an implementation of Monetemurro and Zanette's algorithm for calculating the distribution entropy of words in a body of text.  http://www.worldscientific.com/doi/abs/10.1142/S0219525910002530 This code was originally written to evaluate the algorithm, and probably needs to be refactored before being included in NLTK - in particular, I's like suggestions for a better API