tree.rb 0.3.0

(This gem was named as treevisitor) tree.rb is a 'clone' of tree unix command. The gem implements a library to mange tree structures. The gem contains also a library to build tree with a dsl (domain specific language), and an implementation of visitor design pattern. An example of DSL to build tree: <pre> tree = TreeNode.create do node "root" do leaf "l1" node "sub" do leaf "l3" end node "wo leaves" end </pre>