target-option in menu items not handled on generated pages

[vchrizz]

I would like to open a menu item in a new window, so added '_blank' to the menu items option 'target', but the generated page does not have target="_blank" in HTML source. When using the 'target' of a menu item, it seems its ignored on generated pages. In data/menu/primary.json the target gets set, but then not generated it seems.