Some initial work on positioning
Add support for ranksep
Use lowercase for marginx and marginy keys
Work to hook up all of the pieces that go into layout

We now have a very trivial layout working. Edges not done yet.
Bug fix for centering vertically in each rank
Add test for insertion-independence in verticalAlignment
More testing for layout
More layout testing
Add layout to the benchmark script
Don't export run method for order and position