message: workspace: export Members as part of the public interface
  This struct is returned by `Workspace::members`, but there's no way to
  refer to it since it's not exported.
diff: @@ -9,7 +9,7 @@ pub use self::resolver::Resolve;
  pub use self::shell::{Shell, Verbosity};
  pub use self::source::{Source, SourceId, SourceMap, GitReference};
  pub use self::summary::Summary;
  -pub use self::workspace::{Workspace, WorkspaceConfig};
  +pub use self::workspace::{Members, Workspace, WorkspaceConfig};
  pub mod source;
  pub mod package;
  