Another attempt at getting the API nice

Lots of stuff broken, but we have basic multi-edge support and
performance is much better (so far) than 1.0.0-dev2.
Test for multi-edge key
Remove more old code + add more functionality
Fix up names in benchmark
Implementation for edges and adjacent nodes
Use strict for graph
Rename nodes, edges to allNodes, allEdges
Remove lib/util
Add test for adding nodes with edge keys
Fix to benchmark
Reorder tests to better match code order
Add a path creation function
Add function to get multiple nodes
Small speedup to predecessors / successors
Refactor the graph API to make it easier to work with edges
Add some tests for multigraph edge queries
More multigraph testing
Performance improvements
Add sources and sinks functions
Finished migrating all algs