Returns a specification to start this module under a supervisor.

See Supervisor.

@spec get_database(atom()) :: map() | nil

Returns state information for a specific database

@spec loaded_databases() :: [atom()]

Returns a list of all completely loaded databases.

@spec registered_databases() :: [atom()]

Returns a list of all registered databases.

Registered databases may or may not be already loaded.

@spec set_loaded(atom()) :: :ok | {:error, atom()}

Sets a database's state to :loaded.