xrange to range, for Py3
More Py3 updates and other revisions (near complete)

* Restoration of metanl.general, primarily for untokenize (which is
  still a mess, but it's all we have at the moment)

* Use of unicode_literals in most files to remove the need to mark
  strings as u''.

* Replacement of metanl.general.tokenize_list with
  nltk.wordpunct_tokenize.  Replacement of preprocess_text with
  ftfy.fix_text.

* Removal of various methods to get word frequency and wordlists.

* Removal of commented-out debugging lines, and some pep8 changes.
Further Py3 updates (still need Py2 checks)

* Some fixes to things missed: u'', imports, unicode() vs str(),
  xrange, etc.

* self.process.stdin.flush() added to extprocess.send_input()