function toBlob(node, options) {
    options = options || {}
    options.escapePercentSign = true
    return draw(node, options).then(util.canvasToBlob)
  }
@param {Node} node - The DOM Node object to render
@param {Object} options - Rendering options, @see {@link toSvg}
@return {Promise} - A promise that is fulfilled with a PNG image blob