Function grid

Creates a square grid based at a center point, with cells having spacing height and width.

It fits in as many cells as it can within width and height.

Returns a SVG group, consisting of horizontal and vertical lines

grid(parent, center, spacing, width, height, opts?): SVGGElement
Parameters
- parent: SVGElement
  Parent element
- center: Point
  Center point of grid
- spacing: number
  Width/height of cells
- width: number
  How wide grid should be
- height: number
  How high grid should be
- opts: LineDrawingOpts = {}
Returns SVGGElement