function LayoutBuilder(pageSize, pageMargins, imageMeasure) {
		this.pageSize = pageSize;
		this.pageMargins = pageMargins;
		this.tracker = new TraversalTracker();
	    this.imageMeasure = imageMeasure;
	    this.tableLayouts = {};
	}
Creates an instance of LayoutBuilder - layout engine which turns document-definition-object
into a set of pages, lines, inlines and vectors ready to be rendered into a PDF

@param {Object} pageSize - an object defining page width and height
@param {Object} pageMargins - an object defining top, left, right and bottom margins