added sankey diagram
fixed node_accessor in sankey diagram
added description and tests for sankey diagram
Merge branch 'master' of github.com:andreaferretti/paths-js

Conflicts:
	bower.json
	dist/global/paths.js
	dist/node/package.json
	package.json
fixed merge
Merge pull request #6 from pazqo/master

Added Sankey diagrams.