Resolve "Specify internal input/output dependencies of an Operation"

Closes #74 (closed)

test/test_depends.py

+from b_asic import Addition, Butterfly
+
+class TestDepends:
+    def test_depends_addition(self):
+        add1 = Addition()
+        assert set(add1.inputs_required_for_output(0)) == {0, 1}
+
+    def test_depends_butterfly(self):
+        bfly1 = Butterfly()
+        assert set(bfly1.inputs_required_for_output(0)) == {0, 1}
+        assert set(bfly1.inputs_required_for_output(1)) == {0, 1}
+
+    def test_depends_sfg(self, sfg_two_inputs_two_outputs):
+        assert set(sfg_two_inputs_two_outputs.inputs_required_for_output(0)) == {0, 1}
+        assert set(sfg_two_inputs_two_outputs.inputs_required_for_output(1)) == {0, 1}
+
+    def test_depends_sfg_independent(self, sfg_two_inputs_two_outputs_independent):
+        assert set(sfg_two_inputs_two_outputs_independent.inputs_required_for_output(0)) == {0}
+        assert set(sfg_two_inputs_two_outputs_independent.inputs_required_for_output(1)) == {1}
\ No newline at end of file