Merge or stitch networks

[tomalrussell]

Function to join networks at shared nodes

• assuming a network has been split - perhaps geographically or by network layer - and there are shared nodes at border-crossings or junctions
• join the node and edge lists
• identify shared nodes (by unique ID? by shared location? also by "border" flag?) and ensure they are not duplicated in the result
• identify network component labels if present in the parts, and update component labelling. This needs a little care in implementation - joining parts may join multiple components.