Should there be a lineSegment primitive?

It's often awkward and confusing to use `polyline` to get a single line. Perhaps there should exist primitives `lineSegment` and `thickLineSegment` that take exactly two coordinate pairs as arguments (or just four numbers?), and produce a line segment.

Note that the other polygonal-style shapes: `polygon`, `curve`, and `closedCurve` and their thick and solid variants, depend on having at least three points, so there would be no need to do the same there.

Empieza leyendo las primitivas existentes polyline, polygon, curve y closedCurve en la base de código de Haskell. Determina si dos pares de coordenadas o cuatro números encajan en la API existente; después, define el comportamiento correspondiente de lineSegment y thickLineSegment y verifica que un solo segmento ya no requiera polyline.

Escrito por el modelo de indexación a partir del texto del issue.