interface -> io_nodes, io_loc fix

tests/test_bench.py

@@ -12,4 +12,4 @@ def test_b01(mydir):
 def test_simple():
     c = bench.parse('input(a, b) output(z) z=and(a,b)')
     assert len(c.nodes) == 4
-    assert len(c.interface) == 3
+    assert len(c.io_nodes) == 3

tests/test_circuit.py

@@ -57,9 +57,9 @@ def test_circuit():
     assert 'in1' in c.cells
     assert 'and1' not in c.cells
 
-    c.interface[0] = in1
-    c.interface[1] = in2
-    c.interface[2] = out1
+    c.io_nodes[0] = in1
+    c.io_nodes[1] = in2
+    c.io_nodes[2] = out1
 
     and1 = Node(c, 'and1', kind='and')
     Line(c, in1, and1)