py/obj: Add support for __float__ and __complex__ functions.

tests/float/float_dunder.py

@@ -0,0 +1,42 @@
+# test __float__ function support
+
+
+class TestFloat:
+    def __float__(self):
+        return 10.0
+
+
+class TestStrFloat:
+    def __float__(self):
+        return "a"
+
+
+class TestNonFloat:
+    def __float__(self):
+        return 6
+
+
+class Test:
+    pass
+
+
+print("%.1f" % float(TestFloat()))
+print("%.1f" % TestFloat())
+
+
+try:
+    print(float(TestStrFloat()))
+except TypeError:
+    print("TypeError")
+
+
+try:
+    print(float(TestNonFloat()))
+except TypeError:
+    print("TypeError")
+
+
+try:
+    print(float(Test()))
+except TypeError:
+    print("TypeError")