function load_image_simple(src) {
	return new Promise((resolve, reject) => {
		const img = new Image();

		img.onload = () => { resolve(img); };
		img.onerror = () => { reject(new Error(`failed to load image from ${src}`)); };

		img.src = src;
	});
}
not to be confused with load_image_from_uri
@param {string} src  URI of an image
@returns {Promise<HTMLImageElement>}  an image element