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
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
Added `parse` method to malt.py, fixes #682
Merge pull request #683 from heatherleaf/develop

Added `parse` method to malt.py, fixes #682
Fix for issue #685