methods for punctuation attachment
moved new stuff to separate files for easier merging (dependencies probably wrong)
Merge branch 'master' into punctuation
Merge branch 'master' into punctuation
remove get_coindex (superseeded by parse_label)
Merge branch 'master' into punctuation
incorporated changes from master
Merge branch 'master' into punctuation
moved add_topnode to transform module
new test for add_topnode
delete terminals
method for low punctuation attachment
symetric punctuation attachment and terminal insertion
removal of traces in the penn treebank
ptb label functions
unit tests
insert_terminals tests
better test for insert_terminals, disallow double indices
get left sibling of a tree
corrected left_sibling