Extend "Custom stores" example & tutorial

Extended custom store example for passing data to a method.

site/content/examples/07-stores/04-custom-stores/App.svelte

@@ -6,4 +6,5 @@
 
 <button on:click={count.increment}>+</button>
 <button on:click={count.decrement}>-</button>
+<button on:click={() => count.change(12)}>set to 12</button>
 <button on:click={count.reset}>reset</button>

site/content/examples/07-stores/04-custom-stores/stores.js

@@ -7,6 +7,7 @@ function createCount() {
 		subscribe,
 		increment: () => update(n => n + 1),
 		decrement: () => update(n => n - 1),
+		change: (parameter) => set(parameter),
 		reset: () => set(0)
 	};
 }

site/content/tutorial/08-stores/05-custom-stores/app-a/App.svelte

@@ -6,4 +6,5 @@
 
 <button on:click={count.increment}>+</button>
 <button on:click={count.decrement}>-</button>
+<button on:click={count.change}>set to 12</button>
 <button on:click={count.reset}>reset</button>

site/content/tutorial/08-stores/05-custom-stores/app-a/stores.js

@@ -7,6 +7,7 @@ function createCount() {
 		subscribe,
 		increment: () => {},
 		decrement: () => {},
+		change: () => {},
 		reset: () => {}
 	};
 }

site/content/tutorial/08-stores/05-custom-stores/app-b/App.svelte

@@ -6,4 +6,5 @@
 
 <button on:click={count.increment}>+</button>
 <button on:click={count.decrement}>-</button>
+<button on:click={() => count.change(12)}>set to 12</button>
 <button on:click={count.reset}>reset</button>

site/content/tutorial/08-stores/05-custom-stores/app-b/stores.js

@@ -7,6 +7,7 @@ function createCount() {
 		subscribe,
 		increment: () => update(n => n + 1),
 		decrement: () => update(n => n - 1),
+		change: (parameter) => set(parameter),
 		reset: () => set(0)
 	};
 }

site/content/tutorial/08-stores/05-custom-stores/text.md

@@ -4,7 +4,7 @@ title: Custom stores
 
 As long as an object correctly implements the `subscribe` method, it's a store. Beyond that, anything goes. It's very easy, therefore, to create custom stores with domain-specific logic.
 
-For example, the `count` store from our earlier example could include `increment`, `decrement` and `reset` methods and avoid exposing `set` and `update`:
+For example, the `count` store from our earlier example could include `increment`, `decrement`, `change` and `reset` methods and avoid exposing `set` and `update`:
 
 ```js
 function createCount() {
@@ -14,6 +14,7 @@ function createCount() {
 		subscribe,
 		increment: () => update(n => n + 1),
 		decrement: () => update(n => n - 1),
+		change: (parameter) => set(parameter),
 		reset: () => set(0)
 	};
 }