docs: Update commiter guide.
Add ex_create_subscription method to CloudSigma driver. Also modify
subscription class so the amount attribute is an int.
Add auto_renew attribute to subscription class.
Include subscribed_object attribute on the Subscription class.
Allow user to create server with VLAN.
docs: Add an example of how to create a server with a vlan.
Add a test case for creating a node with VLAN.