Update types to accept SVGElement | HTMLElement in the constructor

[pshihn]

I have been using this lib with SVGElements and it works great, but I always need to cast the element to any because constructor takes in HTMLElement.

Bonus feature: Also perform getScreenCTM inverse calculation when SVG, to create clientX, clientY in SVG viewport's coordinate system. When using scaled SVGs, I often do the following:

const point = svg.createSVGPoint();
point.x = changed[0].clientX;
point.y = changed[0].clientY;
const coords = point.matrixTransform(svg.getScreenCTM().inverse());