Charmcraft bases & provider support

[cjp256 (Chris Patterson)]

@heitor series is being deprecated in favor of bases support:

Charm Metadata v2

Post superceded by: Juju | Charm Metadata Reference Charm Metadata Reference Type: Meta Serialized location: /metadata.yaml Field Since Default Description name string - required Name of the charm. summary string - required A short one line summary of the charm. description string - required A full description of the charm, can be multiple lines. maintainers []string - nil List of maintainers in the formation “First Last ”. terms []string - nil List of terms a charm user must…