Fix typings

[saraedum]

Typescript otherwise complains in my setup:

515:21 Parameter 'MultilineEdgeShape' implicitly has an 'any' type.
    513 |     class MultilineEdge extends Edge {
    514 |         shape: MultilineEdgeShape;          // there may be only one line edge and only terminal ray edges
  > 515 |         constructor(MultilineEdgeShape);
        |                     ^
    516 |     }
    517 |
    518 |     class Multiline extends LinkedList {
541:14 'point', which lacks return-type annotation, implicitly has an 'any' return type.
    539 |
    540 |     function point(x?: number, y?: number): Point;
  > 541 |     function point(arr?: [number, number]);
        |              ^
    542 |     function circle(pc: Point, r: number) : Circle;
    543 |     function line(pt?: Point, norm?: Vector) : Line;
    544 |     function line(norm?: Vector, pt?: Point) : Line;

[coveralls]

Coverage remained the same at 82.433% when pulling 8fba716 on saraedum:patch-1 into 7323efb on alexbol99:master.