Rename "nodedata" members to "nd" (as per modifiers, for less typing)
First attempt at a datatype to represent relationships (i.e. node links)

* We need a way of sharing relations between the nodes which use it. The
  current design assumes that one link is shared between the two nodes
  which use it. Saves mem but induces higher traversal cost?
* The relationship types enum is used to provide additional metadata about
  a link, specifically, if the type of data we're interested in reside there
First pass at connecting links to nodes

* Nodes store ref-lists to the DepsRelation link data stored in a buffer
  on toplevel of the graph.
* Also, added member to DepsNode for tracking the number of inlink nodes
  which still have yet to be evaluated...