[REWRITE] second attempt: removed need of duplicate data.
[REWRITE] second attempt: removed need of duplicate data.

This new version uses a single node with both link and data information.
It features smaller memory footprint and faster operations. Also, less
copies are performed during updates.

The interface changed a bit, and a generic node appears inside typed nodes,
but all can be cast into another one.

sociomantic-tsunami/ebtree,haproxy/ebtree,sociomantic-tsunami/ebtree