Set version to 0.5.0-pre
Initial work on nesting graphs
Add cleanup for nesting graph
Function to remove empty ranks
Make simplify copy the graph object
Don't create a self loop for the root in nesting graph
Hook up nesting graph to rank function
Fix up benchmarks
Add function to get a non-compound graph
Don't position subgraph nodes
More work to integrate subgraph functionality into layout
Move some rank utils up one level
Don't re-render unless the input has changed
Get ranker option from graph directly
Make space for edge labels
Position no longer has the ranksep default
Add initial support for edge labels to normalize
Edge labels are now part of layout