Object::Unit: changed slug length limit to 255.
IO::Datastore: doc tidy.
Cmd::Stage: renamed is_local() to is_client().¹

1: Stage doesn't really know about the context.
System::Context: added is_local(), is_remote() and initiator variants for stages.
Cmd::Status: clarified action taken due to an explicit error.
System::Context: implemented rudimentary command termination.