topological sorting. of stuff.
Version bump.
We need to be able to generate an ordering for _any_ DAG, not just for a DAG with a given root.
Avoid generating the same node twice, once as the last entry of the children, once as the root during recursion.
Testing for a correct topological sorting of a DAG.
Example set of DAGs
Test for a fixed set of DAGs
Added a length property to test the topological sorting
Version bump
Merge branch 'master' into topological_sort

Conflicts:
	setup.py
Merge pull request #104 from itkovian/topological_sort

Topological sort
Merge branch 'master' into ConstantDict

Conflicts:
	test/missing.py
replace ConstantDict with FrozenDictKnownKeys, update unit tests