    V.rectToPath(r)

Convert a rectangle `r` to SVG path commands. `r` is an object of the form `{ x: [number], y: [number], width: [number], height: [number], top-ry: [number], top-ry: [number], bottom-rx: [number], bottom-ry: [number] }` where `x, y, width, height` are the usual rectangle attributes and `[top-/bottom-]rx/ry` allows for specifying radius of the rectangle for all its sides (as opposed to the built-in SVG rectangle that has only `rx` and `ry` attributes).