':param filename: a name of a file in Malt-TAB format
:param zero_based: nodes in the input file are numbered starting from 0
rather than 1 (as produced by, e.g., zpar)
:param str cell_separator: the cell separator. If not provided, cells
are split by whitespace.
:param str top_relation_label: the label by which the top relation is
identified, for examlple, `ROOT`, `null` or `TOP`.
:return: a list of DependencyGraphs'

@staticmethod
def load(filename, zero_based=False, cell_separator=None, top_relation_label=u'ROOT'):

    with open(filename) as infile:
        return [DependencyGraph(tree_str, zero_based=zero_based, cell_separator=cell_separator, top_relation_label=top_relation_label) for tree_str in infile.read().split(u'\n\n')]
