filters: refactored get_filtered_candidates() using node_attrs()
filters: refactored morph_agreement() using node_attrs()
filters: fixed is_bound() and refactored it w/ node_attrs()

fixes
- wrong call to anaphora_boundaries()
- syntax error in sent_length calculation
- wrong return value of anaphora_boundaries()
filters: changed lemma_attrib default val in is_coreferent(); refactored w/ node_attrs();
filters: changed lemma_attrib default val in is_coreferent()...
- fixed call to traverse_dependencies_up()
- refactored w/ node_attrs()
main: fixed imports
main: added proper description to Pocores.entities
main: added Pocores.mentions map (mapping from each mention to its entity)
added node_attrs() helper function to access docgraph token/sentence attributes
main: refactored _get_sentence() w/ node_attrs()
main: refactored _get_entity_grid() and print_entity_grid()
resolve_anaphora: fixed call to is_expletive; refactored w/ node_attrs()
main: fixed _resolve_nominal_anaphora() using Pocores.mentions dict
main: fixed _resolve_pronominal_anaphora() / refactored it
- fixed adding stuff to Pocores.entities and Pocores.mentions
- if -> elif
- fixed call to refactored get_distance() function
reimplemented output_with_brackets() function; added mintok/maxtok helpers
main: minor flake8
preferences: (re)implemented get_depth() using traverse_dependencies_up()
preferences: (re)implemented get_chain_lenght() using Pocores.mentions
preferences: (re)implemented check_parallelism()
preferences: (re)implemented check_role()