* d3-sankey:
* Initial incomplete draft of definitions (see TODOs) In particular issue with circular definitions given the source code approach to mutating nodes and links.
* Added tsconfig and tslint.
* Added initial draft of shape tests
* Subject to addressing SankeyNodes/SankeyLinks circularity in definitions
* Fixed return types of nodes() and links() to reflect source code rather than API Doc.
* Use intersection types to avoid circularity
* Using intersection types avoids running into the circularity issue with the generics driving SankeyNode an SankeyLink
* Refine SankeyLinkPathGenerator tests.
* Add interface tests for SankeyNode and SankeyLink
* Complete comments. Add one pathGen test.
* Fix lint errors.
* semicolon.
* Updated some comments.
* Some comments were updated to reflect the comments used in PR 23 to the d3-sankey repo
* Fix typo. Thx @gustavderdrache .
* Add Co-Maintainer
