Add method 'contains' to Box

What's Changed

• Implementation of 'contains' relation between point and box. by @delmohf in #111
• Box inflate by @delmohf in #113
• Add method 'contains' to Box by @alexbol99 in #160
• Add ability to insert entry to PlanarSet in the form {key: Box, value: Shape}, like

  let planarSet = new PlanarSet();
  let segment = new Segment(1,2,4,5);
  let circle = new Circle(new Point(3,3), 5);
  planarSet.add({key: segment.box, value: segment});
  planarSet.add({key: circle.box, value: circle});

This change enables to store in PlanarSet shapes that are not part of flatten-js

Full Changelog: v1.4.7...v1.4.8