BEA workshop release

Updated version of L2-UD including the work presented at the 18th Workshop on Innovative Use of NLP for Building Educational Applications (paper: Towards automatically extracting morphosyntactical error patterns from L1-L2 parallel dependency treebanks):

• still in-progress, but much more advanced automatic pattern extraction (extract command)
• example retrieval (example command)
• simplified pattern matching (match command)

L1-L2 treebank query engine

• first full implementation of the match command for querying L1-L2 treebanks for specific error patterns
• in-progress implementation of the extract command for extracting all error patterns from L1-L2 treebanks