Several fizes and features added from networkD3 and pull requests

- has several modifications from networkD3 sankey.js
- included fixes and features from unmerged pull requests:
- d3/d3-plugins#124: Fix nodesByBreadth to have proper ordering
- - d3/d3-plugins#120: Added 'l-bezier' link type
- d3/d3-plugins#74: Sort sankey target links by descending slope
- d3#4: Add horizontal alignment option to Sankey layout
- added option numberFormat, default being ",.5g" (see , fixes
christophergandrud/networkD3#147)
- added option NodePosX, fixes christophergandrud/networkD3#108
- added option to force node ordering to be alphabetical along a path
(only works well with trees with one parent for each node, but might fix
christophergandrud/networkD3#153)