Instances#

Game directories managed from a modpack and from projects added on their own.

`Instance`	A game directory whose contents come from a modpack and added projects.
`Changes`	What a change to an instance would do, or did.
`InstanceState`	What an instance holds, as of its last change.

Additions#

`Plan`	What `Instance.add` would install.
`Addition`	A project installed on its own, rather than by the instance's pack.
`ContentFile`	A mod, resource pack or shader pack in an instance.