Support SVG tag attributes

[morki]

It would be useful to support SVG attributes like:

public var SVG.viewBox: String
    get() = stringAttribute[this, "viewBox"]
    set(viewBox) {
        stringAttribute[this, "viewBox"] = viewBox
    }

public var SVG.width: String
    get() = stringAttribute[this, "width"]
    set(width) {
        stringAttribute[this, "width"] = width
    }

public var SVG.height: String
    get() = stringAttribute[this, "height"]
    set(height) {
        stringAttribute[this, "height"] = height
    }