Added Google Analytics to the documentation site
Moving a node to a different tree at the same left position was ineffective
In certain conditions deleting a node in a tree will modify nodes
in different trees.

If there were nodes in different trees with a rgt value higher than
the rgt value of the deleted node, their lft/rgt values were
wrongly modified.

Thanks to Ramon Ackermann <ramon.ackermann@gmail.com> for
discovering this insidious bug.
Updated version to 1.3.1