Instance Support
Added InstanceBase which the endpoint Containers, Intsances & VM's extend,
/instances/ was introduced in 3.19 and is a transparent way to access both virtual machines and containers
If you want just containers use Containers
If you want just virtual machines use VirtualMachines
If you want both containers & virtual machines use Instance
If your host doesn't support Instances it will fall back to containers instead so its safe to use instances if in the future you plan to update LXD and use virtual machines!