Support aliasing within the glide tag directly

This makes the following type of Blade template "Just Work":

```blade
<s:glide :src="$multiple_assets" width="600" as="assets">
  @foreach ($assets as $asset)
    {{ $asset['url'] }}
  @Endforeach
</s:glide>
```

src/Tags/Glide.php

@@ -119,7 +119,7 @@ public function dataUri()
      *
      * Generates the image and makes variables available within the pair.
      *
-     * @return string
+     * @return string|array
      */
     public function generate($items = null)
     {
@@ -131,7 +131,11 @@ public function generate($items = null)
 
         $items = is_iterable($items) ? collect($items) : collect([$items]);
 
-        return $items->map(function ($item) {
+        if ($alias = $this->params->get('as')) {
+            unset($this->params['as']);
+        }
+
+        $items = $items->map(function ($item) {
             try {
                 $data = ['url' => $this->generateGlideUrl($item)];
 
@@ -150,6 +154,14 @@ public function generate($items = null)
                 \Log::error($e->getMessage());
             }
         })->filter()->all();
+
+        if ($alias) {
+            return [
+                $alias => $items,
+            ];
+        }
+
+        return $items;
     }
 
     /**