Toy example (Guillaume)

See merge request !13

A new rdbgui4sasa with automatic daemons

See merge request !14

Fix: the Register.diameter returned the links number (introduced in sha:40eece7c)

- add sub_tree_size, parent, is_in_tree, is_out_tree
- fix height (was only working for out-trees)
- a predessors to Topology.t
- refactor a lot of strange things in the code
  - in the use of hashtbl in particular