Minimal d3js line smoothing, topojson version

Minimal line smoothing topojson version, in answer to Making a SVG path like a smooth line instead of being ragged. The idea of d3.svg.line together with interpolations of y coordinates for lins smoothing is from E.Meeks. This blocks is a minimal stand alone case study to build upon.

Notes:

• While .interpolate("cardinal") is used, we actually have ["linear", "cardinal", "basis", "monotone", "step-before"] methods, as shown in E.Meeks advanced demo. E. Meeks explain his approach here.
• The data quantisation, simplification and zoom (aka scale) should be suitable.
• Artefacts may appears if the antimeridian is crossed. An other world map, also crossing this antimeridian, did not display this artifact.