async function srvSave(key, serialized) {
	return await fetch(`${svrApi}/${key}`, {
		method: 'POST',
		headers: { 'Content-Type': 'application/json;charset=utf-8'	},
		body: JSON.stringify(serialized)
	});
}
@param {string} key
@param {DiagramSerialized} serialized
@returns {Promise}