Minor bugfixes
Merge branch 'master' of https://github.com/nltk/nltk
Implemented span_tokenize() method for PunktWordTokenizer.
Added doctest for span_tokenize in docstring of the PunktWordTokenizer class.
Merge pull request #520 from huderlem/master

Implemented span_tokenize() method for PunktWordTokenizer.
Fixed bug in path of grammar files; fixed relative import statements
Merge branch 'master' of https://github.com/nltk/nltk