Nltk-ma

* Code:
- bugfixes, including fixed bug in Brown corpus reader
- cleaned up wordnet 2.1 interface code and similarity measures
- support for full Penn treebank format contributed by Yoav Goldberg
* Tutorials:
- expanded tutorials on advanced parsing and structured programming
- checked all doctest code
- improved images for chart parsing

* Code:
- expanded semantic interpretation package
- new high-level chunking interface, with cascaded chunking
- split chunking code into new chunk package
- updated wordnet package to support version 2.1 of Wordnet.
- prototyped basic wordnet similarity measures
(path distance, Wu + Palmer and Leacock + Chodorow, Resnik similarity measures.)
- bugfixes (tag.Window, tag.ngram)
- more doctests
* Contrib:
- toolbox language settings module
* Tutorials:
- rewrite of chunking chapter, switched from Treebank to CoNLL format as main focus,
simplified evaluation framework, added ngram chunking section
- substantial updates throughout (esp programming and semantics chapters)
* Corpora:
- Chat-80 Prolog data files provided as corpora, plus corpus reader

* Code:
- more doctest
- code to read Chat-80 data
- HMM bugfix
* Tutorials:
- continued updates and polishing
* Corpora:
- toolbox MDF sample data

* Code:
- new toolbox module (Greg Aumann)
- new semantics package (Ewan Klein)
- bugfixes
* Tutorials
- substantial revision, especially in preface, introduction, words,
and semantics chapters.

* Code:
- bugfixes (probability, shoebox, draw)
* Contrib:
- new work on shoebox package (Stuart Robinson)
* Tutorials:
- continual expansion and revision, especially on introduction to
programming, advanced programming and the feature-based grammar chapters.

* Code:
- improvements to shoebox module (Stuart Robinson, Greg Aumann)
- incorporated feature-based parsing into core NLTK-Lite
- corpus reader for Sinica treebank sample
- new stemmer package
* Contrib:
- hole semantics implementation (Peter Wang)
- Incorporating yaml
- new work on feature structures, unification, lambda calculus
- new work on shoebox package (Stuart Robinson, Greg Aumann)
* Corpora:
- Sinica treebank sample
* Tutorials:
- expanded discussion throughout, incl: left-recursion, trees, grammars,
feature-based grammar, agreement, unification, PCFGs,
baseline performance, exercises, improved display of trees