Merge pull request #3 from nltk/master

Merge updates from NLTK master
bug in chat80 doctest
fixed bug in FreqDist.max() (erroneously returned (maxkey, maxval) instead of maxkey)
added subpackaging structure (empty; demo still runs)
major refactoring without change in functionality
major refactoring without change in functionality (11 files, 4 subpackages)
removed cruft from IDE
added dummy arguments to abstract methods  __eq__, __ne__ (to suppress warnings)
added kw argument ruleformat to the brill trainer, controlling the rule output format
added new class Feature, multififeature Template and revised Rule
added demo for the new features
deleted unused parameter 'radius'
added methods for collecting and printing rule and template statistics
cleaned up example features Word and Tag
added computed defaults for yaml_tag and PROPERTY_NAME
added computation of defaults for yaml_tag and PROPERTY_NAME to base class Feature
added describe_template_sets() for a dynamically computed description of the available sample template sets
updated docstrings
added Template.expand() and Feature.expand(), facilitating mass generation of Templates. Updated docs
template statistics now can be computed (and sorted) on provided test data, making an interesting comparison with the training