migrate from python3 (#12)

FEATURES:

- add `UCDN` product

ENHANCEMENTS:

- Add toolkit for auto release

Author: yufeiminds

docs/services.rst

@@ -1,12 +1,6 @@
 UCloud SDK Services
 ===================
 
-PathX
------
-
-.. autoclass:: ucloud.services.pathx.client.PathXClient
-   :members:
-
 StepFlow
 --------
 
@@ -19,6 +13,12 @@ UAccount
 .. autoclass:: ucloud.services.uaccount.client.UAccountClient
    :members:
 
+UCDN
+----
+
+.. autoclass:: ucloud.services.ucdn.client.UCDNClient
+   :members:
+
 UDB
 ---
 
@@ -73,9 +73,3 @@ USMS
 .. autoclass:: ucloud.services.usms.client.USMSClient
    :members:
 
-VPC
----
-
-.. autoclass:: ucloud.services.vpc.client.VPCClient
-   :members:
-