Namespace tree structure for Uuid

[bvssvni]

The current design does not support multiple children per sprite, but this can be supported by adding a separate namespace tree structure.

pub struct Namespace {
    /// Stores names and corresponding Uuid.
    names: Vec<(String, Uuid)>,
    /// Maps from Uuid to name index.
    from_name_index: HashMap<Uuid, uint>,
    /// Stores sub node ranges.
    sub_node_ranges: Vec<Uuid>,
    /// Points to a range in `sub_node_range`.
    in_sub_node_ranges: HashMap<Uuid, (uint, uint)>,
}