Add collection extractor

docs/Extractors/Collection.md

@@ -0,0 +1,28 @@
+# Collection Extractor
+
+The collection extractor can be used to get data from any iterable item. It accepts arrays or traversables objects. The collection items must be associative arrays.
+
+> **Tip:** Using generators will decrease memory usage.
+
+## Options
+
+| Name | Type | Default | Description |
+| ---- |----- | ------- | ----------- |
+| columns | array | null | Columns that will be extracted. |
+
+
+## Usage
+
+Default options:
+```php
+$etl->extract('collection', $iterable);
+```
+
+Custom options:
+```php
+$options = [
+    'columns' => ['id', 'name']
+];
+
+$etl->extract('collection', $iterable, $options);
+```

docs/Extractors/README.md

@@ -1 +1,3 @@
 # Extractors
+
+* [Collection](Collection.md)

docs/README.md

@@ -1,3 +1,4 @@
 * [Introduction](Introduction.md)
 * [Getting Started](GettingStarted.md)
 * [Extractors](Extractors/README.md)
+    * [Collection](Extractors/Collection.md)