Parameters
	----------
	nltk_tokenizer : nltk.tokenize.* instance (e.g., nltk.TreebankWordTokenizer())

	Returns
	-------
	Doc of tweets

	Notes
	-------
	Requires NLTK to be installed

def nltk_tokenzier_factory(nltk_tokenizer):
	'''
	Parameters
	----------
	nltk_tokenizer : nltk.tokenize.* instance (e.g., nltk.TreebankWordTokenizer())

	Returns
	-------
	Doc of tweets

	Notes
	-------
	Requires NLTK to be installed
	'''

	def tokenize(text):
		toks = []
		for tok in nltk_tokenizer.tokenize(text):
			if len(tok) > 0:
				toks.append(Tok(_get_pos_tag(tok),
				                tok.lower(),
				                tok.lower(),
				                ent_type='',
				                tag=''))
		return Doc([toks], text)

	return tokenize