Simple dependency tree builder, handles forward and reverse dependencies, returning an ordered tree with its nodes ordered from root towards leafs.
Example:
>>> from disentangler import Disentangler
>>> inst = Disentangler.new()
>>> inst.add('a', {})
>>> inst.add('b', {'depends_on': ['d', 'c']})
>>> inst.add('c', {})
>>> inst.add('d', {'depends_on': ['a']})
>>> ordered = inst.solve()
>>> print(ordered)
OrderedDict([('a', {}),
('c', {}),
('d', {'depends_on': ['a']}),
('b', {'depends_on': ['d', 'c']})])