changed ContextFreeGrammar to CFG, WeightedGrammar to PCFG, and StatisticalGrammar to ProbabilisticGrammar
renaming LogicParser.parse to Expression.fromstring, for consistency with the rest of NLTK, cf issue https://github.com/nltk/nltk/issues/656
drop the string initialization of Tree
drop the string initialization of Tree
drop the string initialization of Tree
drop the string initialization of Tree
fixed & updated collocations unit tests
use the original likelihood values from Dunning, CL, 1993, not sure why the values are x2 the original, they weren't present in the paper
fixed wordnet doctests now that using a list of languages are deprecated
Merge pull request #678 from jskda/pull_request.tests

Fixes to collocation unit tests
Merge pull request #676 from stevenbird/issue/657

Names for grammar classes
read `lemma`, `ctag` and `feats` columns from conll file
Merge pull request #677 from jw2013/develop

Drop the string initialization of Tree
Merge pull request #679 from nournia/conll-format

CONLL format missed columns
updated ChangeLog with info re new changes
Modified DRT module to support fromstring-style initialisation, cf https://github.com/nltk/nltk/issues/656
added missing qualifier so that classmethod can access class variable, cf cf https://github.com/nltk/nltk/issues/656
Modified Linear Logic module to support fromstring-style initialisation, cf https://github.com/nltk/nltk/issues/656
tweak docs; fix reference to _LogicParser
Merge branch 'develop' into issue/656