Before this commit, there were situations where the reference numbers
were not properly set, which caused the blocks generated to crash
because the algorithm could not get correct references.
Synthetic handler is a sort of event delegation that allows placing
only one listener on the document to improve performance. It is an opt-in option.
Native listener places the listener on the node itself.
We reintroduce the possibility to mount the app in first position in
a target. The option "self" has been dropped since it is now possible
for a component to have several top level nodes.
Géry Debongnie