'Creates a new LineDiff object. Note that a line cannot be
changed _and_ deleted at the same time.
:param change: False or a tuple (original, replacement)
:param delete: True/False
:param add_after: False or a list of lines to append after this ones'

def __init__(self, change=False, delete=False, add_after=False):

    self._delete = False
    self.change = change
    self.delete = delete
    self.add_after = add_after
