IR - Test adding PrintItem::Items and PrintItems::RcItems about dprint

[dsherret]

Not doing this. Instead I'm constructing a graph while parsing the nodes. Should be a lot faster (hopefully) and the parsing API will be better (going back to Signal::X too).

Looks like this:

let mut items = PrintItems::new();

items.push_info(start_info);
items.push_str("class");
items.extend(parse_node(....));
items.push_signal(Signal::NewLine);

items

...which internally builds up graph nodes and connects them together.

[dsherret]

The way better solution was implemented in #56.

Basically when parsing a directional graph is constructed. All paths in that graph are behind an Rc<T> so the paths can be shared. The printer then maintains a "next node stack" to figure out what the next node should be when reaching the end of a path.