Merge pull request #85 from ankurdave/vid-varenc

Always write Vids using variable encoding
Merge pull request #86 from ankurdave/vid-varenc

Finish work on #85
Clean up vTableReplicated in GraphImpl

1. Rename vTableReplicated -> replicatedVertices
2. Factor out ReplicatedVertices.zipWithEdges
3. Update GraphImpl docs
Fix capture in ReplicatedVertices.zipWithEdges