reverting changes to probability.py and removing model package, due to premature…

reverting changes to probability.py and removing model package, due to premature merge of https://github.com/nltk/nltk/commit/504b0f74e32202195592febf525dc7d13bffa9e0 https://github.com/nltk/nltk/commit/4e02bc53c38c56cbe2b7242f0e9171964652382c https://github.com/nltk/nltk/commit/fc40e1611fc905ba2d5d2cc390c882146e2f6a03 https://github.com/nltk/nltk/commit/166983beabed0232a6488e5b7fa33ad72baa8849 https://github.com/nltk/nltk/commit/961565900b08ecb1b3821730c65d07178ad65c1c; cf #871, #800

nltk/model/__init__.py

-# Natural Language Toolkit: Language Models
-#
-# Copyright (C) 2001-2014 NLTK Project
-# Author: Steven Bird <stevenbird1@gmail.com>
-# URL: <http://nltk.org/>
-# For license information, see LICENSE.TXT
-
-from nltk.model.ngram import NgramModel

nltk/model/api.py

-# Natural Language Toolkit: API for Language Models
-#
-# Copyright (C) 2001-2014 NLTK Project
-# Author: Steven Bird <stevenbird1@gmail.com>
-# URL: <http://nltk.org/>
-# For license information, see LICENSE.TXT
-
-
-# should this be a subclass of ConditionalProbDistI?
-
-class ModelI(object):
-    """
-    A processing interface for assigning a probability to the next word.
-    """
-
-    def __init__(self):
-        '''Create a new language model.'''
-        raise NotImplementedError()
-
-    def prob(self, word, context):
-        '''Evaluate the probability of this word in this context.'''
-        raise NotImplementedError()
-
-    def logprob(self, word, context):
-        '''Evaluate the (negative) log probability of this word in this context.'''
-        raise NotImplementedError()
-
-    def choose_random_word(self, context):
-        '''Randomly select a word that is likely to appear in this context.'''
-        raise NotImplementedError()
-
-    def generate(self, n):
-        '''Generate n words of text from the language model.'''
-        raise NotImplementedError()
-
-    def entropy(self, text):
-        '''Evaluate the total entropy of a message with respect to the model.
-        This is the sum of the log probability of each word in the message.'''
-        raise NotImplementedError()
-