Add new trait : CellRenderer
New type : TreePath
Rebase on master
New type : TreeIter
New Type : TreeModel
Fix rebase error
Change CVec to Vec
Merge pull request #70 from GuillaumeGomez/treeview

work on tree view
add menushell interface
uncomment functions in traits::MenuShell
add gtk::SeparatorMenuItem
add gtk::CheckMenuItem trait and widget
restore menuitem