make readable start callback optional

site/content/docs/03-run-time.md

@@ -248,7 +248,7 @@ This makes it possible to wrap almost any other reactive state handling library
 store = writable(value?: any)
 ```
 ```js
-store = writable(value?: any, callback?: (set: (value: any) => void) => () => void)
+store = writable(value?: any, start?: (set: (value: any) => void) => () => void)
 ```
 
 ---
@@ -297,7 +297,7 @@ unsubscribe(); // logs 'no more subscribers'
 #### `readable`
 
 ```js
-store = readable(value: any, callback: (set: (value: any) => void) => () => void)
+store = readable(value?: any, start?: (set: (value: any) => void) => () => void)
 ```
 
 ---

src/runtime/store/index.ts

@@ -50,8 +50,6 @@ const subscriber_queue = [];
  * @param value initial value
  * @param {StartStopNotifier}start start and stop notifications for subscriptions
  */
-export function readable(): Readable<undefined>;
-export function readable<T>(value: T, start: StartStopNotifier<T>): Readable<T>;
 export function readable<T>(value?: T, start?: StartStopNotifier<T>): Readable<T> {
 	return {
 		subscribe: writable(value, start).subscribe