[mod] remove unused function
[mod] reduce indirection of walker
[mod] get rid of useless StopState class
[mod] separate walking and working concepts
[mod] remove useless class for walking tree
[mod] add worker functions when descending tree
[mod] move formatting keys handling in worker
[mod] begin rendering keys indexing at 0
[mod] use rendering_dictionary in dumper
[enh] export rendering dictionnary