Add Line Shapes example to docs

- fig : https://plot.ly/~etpinard/436/linear-spline-vhv-hvh-vh-hv/
- inspired by : https://plot.ly/~alex/315/new-line-shape-options/
Ah, i see, yeah that makes sense then. It might be cool to have the word *interpolation* in there, yeah. I'd imagine that's a common thing to search for. "Shape Options for Interpolation", "Line Shape Options for Interpolation"?