Changes

Summary

1. clarified signature;
2. clarified self_update: imitate visible directory state on remote side;
3. more operations;
4. self_update implies push_isabelle_home (see also 4c253e84ae62);
5. uniform setup_repository (pull/clone without update); tuned signature;
6. clarified signature: facilitate interactive experimentation;
7. clarified tasks;
8. tuned signature;