[evol] virtual attributes support §2 (aspect vattrs with example) (refs #141)
[licence] copyright updated (or added when missing)
[fix/evol] ensure a shadow/object/aspect is not cast(/post-cast) multiple times, and btw correct the raise_error() method
[evol/fix] fixed creation hooks call, hooks->plugins with hooks and simplified hooks, added plugin parameters in config and updated aspect/fs
[cleanup] internal rework #2