merging.py: flake8, shortened inputs w/ __init__
anaphoricity.py: flake8, renamed vars
util.py: flake8, added import errno
rst.py: flake8, string formatting
mmax2.py: flake8, outsourced has_antecedent(markable)
exmaralda.py: flake8, outourced is_informative(layer)