Add network simplex as an option for ranking
Merge exp-rank-fixes branch with simplex branch
Require Digraph to build network simplex spanning tree
Add more descriptive comments
Duplicate ranking tests using network simplex
Adjust ranks as feasible tree changes.  Add test for network simplex ranking
Merge with cpettitt/master
Merge branch 'master' of git://github.com/Concurix/dagre into Concurix-master
Move rank network simplex to lib/rank/simplex

The network simplex algorithm is complex enough that it deserves its own
module. This also gives the ability to test the algorithm directly, if
appropriate.
Consolidate tests for default and network simplex rankers
Merge branch 'master' into Concurrix-network-simplex
Merge branch 'master' into Concurrix-network-simplex

Conflicts:
	lib/rank.js