add tcc

app/lib/irt/test_response_function.py

@@ -0,0 +1,12 @@
+# otherwise known as the Test Characteristic Curve (TCC)
+class TestResponseFunction():
+  def __init__(self, irf):
+    self.irf = irf
+
+  def calculate(self, items, **kwargs):
+    result = 0
+
+    for item in items:
+      result += irf.calculate(b_param=item.b_param, theta=kwargs['theta'])
+
+    return result