Example of how to define custom features in TnT Board.
Modified http://d3js.org/d3.v3.min.js to a secure url
Modified http://tntvis.github.io/tnt.board/build/tnt.board.min.js to a secure url
https://d3js.org/d3.v3.min.js
https://tntvis.github.io/tnt.board/build/tnt.board.min.js