Add Dependency Evaluator to compute Labeled Attachment Score and Unlabeled Attachment Score  #805 

Re-implement http://www.maltparser.org/malteval.html for computing LAS and UAS by adding file nltk.parse.depeval

Train MaltParser on english and czech version of conll share tasks and evaluate on the test data (english_ptb_test.conll and czech_pdt_test.conll). Malt eval and this implementation give the same result. 


This regular expression won't match punctuation in Python. Please make sure your test case has differences in the gold and predicted punctuation to test this.