Nested set: Manipulate a tree node structure stored in MySQL

This class can be used to manipulate an hierarchical tree of node stored in a MySQL database table.

It can perform several types of operations to manipulate database records that represent the nodes the tree.

Currently it can create the root node, insert a node, retrieve a node, retrieve the tree of nodes, display the tree as nested HTML lists, delete a node, get the path of the parents of a node and move nodes to the left or the right.