Add an implementation of _PyType_Name for Python 3.6

This function was introduced in Python 3.7
(https://bugs.python.org/issue31497).

asyncpg/protocol/record/recordobj.c

@@ -14,6 +14,21 @@
 # define _ApgObject_GC_IS_TRACKED PyObject_GC_IsTracked
 #endif
 
+#if PY_VERSION_HEX < 0x03070000
+static const char * _PyType_Name(PyTypeObject *type)
+{
+    assert(type->tp_name != NULL);
+    const char *s = strrchr(type->tp_name, '.');
+    if (s == NULL) {
+        s = type->tp_name;
+    }
+    else {
+        s++;
+    }
+    return s;
+}
+#endif
+
 static PyObject * record_iter(PyObject *);
 static PyObject * record_new_items_iter(PyObject *);