Fixed minor inconsistency in A expansion rule.
changed chunkparser api to use root_label and chunk_label instead of top_node and chunk_node
updates to changelog in preparation for next release
updated chunk documentation for new API; changing chunk_node to chunk_label
dropped generate_iter(), made generate() into an iterator
Changed relative import to absolute.
Tweaked string / byte status of input_str in subprocess call.
Merge branch 'master' of https://github.com/nltk/nltk