Added another callback in typeinfo for handling outer-node queries
New node adding code fleshed out to use typeinfo
Node types registry - Use a GHash for now

This makes it easy when dealing with the types, which can now have arbitrary
codes given to them, instead of having to be tightly packed.

However, this may turn out to be overkill, since we only really have a few
core node types, so using an array may prove to be a better strategy overall...