Module sugar methods

I've added some "sugar" methods to call/cast the NanoRing more easily:

```elixir
NanoRing.all
NanoRing.up
NanoRing.add_node("node@node")
NanoRing.add_node(:"node@node")
NanoRing.del_node("node@node")
NanoRing.del_node(:"node@node")
```

I've also made `update_ring/2` a private method.

What do you think?