Added readme.

Author: Sevavietl

README.md

@@ -0,0 +1,115 @@
+# Array Extensions
+
+This is a collection of array wrappers.
+
+## Composite Key Array
+
+Sometimes it is useful to have ability to access nested value with one,
+array like, key (some questions were asked about this: [on quora](https://www.quora.com/Learning-PHP-Is-there-a-way-to-get-the-value-of-multi-dimensional-array-by-specifying-the-key-with-a-variable), [on stackoverflow](http://stackoverflow.com/questions/22614817/get-a-value-from-a-multidimensional-array-using-the-dot-syntax)).
+
+`CompositeKeyArray` class gives you the ability to do all basic array operations using array-like (nested) key.
+It implemets [`ArrayAccess`](http://php.net/manual/en/class.arrayaccess.php) interface:
+
+### 1. offsetExists:
+
+You can check nested keys for existance.
+
+```php
+    $array = new CompositeKeyArray([
+        'foo' => [
+            'bar' => 'baz'
+        ]
+    ]);
+
+    var_dump(isset($array[['foo', 'bar']])); // => bool(true)
+    var_dump(isset($array[['foo', 'quux']])); // => bool(false)
+```
+
+### 2. offsetGet:
+
+You can get value by nested key. If nested key is not set the `UndefinedOffsetException` will be thrown.
+
+```php
+    $array = new CompositeKeyArray([
+        'foo' => [
+            'bar' => 'baz'
+        ]
+    ]);
+
+    var_dump($array[['foo', 'bar']]); // => string(3) "baz"
+    var_dump($array[['foo', 'quux']]); // => PHP Fatal error:  Uncaught UndefinedOffsetException: Undefined offset quux.
+```
+
+### 3. offsetSet:
+
+You can set value for nested key.
+
+```php
+    $array = new CompositeKeyArray();
+
+    $array[['foo', 'bar']] = 'baz';
+
+    var_dump($array[['foo', 'bar']]); // => string(3) "baz"
+```
+
+There is one pitfall. When you try to do `$array['foo']['bar'] = 'baz'` you get `Indirect modification of overloaded element of CompositeKeyArray has no effect`.
+The reason was explained [here](http://stackoverflow.com/questions/20053269/indirect-modification-of-overloaded-element-of-splfixedarray-has-no-effect). So in order to achive the desired result you have to do the following:
+
+```php
+    $array = new CompositeKeyArray([
+        'foo' => []
+    ]);
+
+    $array['foo']['bar'] = 'baz'; // => PHP Notice:  Indirect modification of overloaded element of CompositeKeyArray has no effect
+
+    var_dump($array['foo']); // => array(0) {}
+
+    $array[['foo', 'bar']] = 'baz';
+
+    var_dump($array['foo']); // => array(1) {["bar"] => string(3) "baz"}
+```
+
+But there is another edge case left: when you need to append element at the end of an array.
+
+```php
+    $array = new CompositeKeyArray([
+        'foo' => []
+    ]);
+
+    $array[[[]]] = 'bar';
+    $array[['foo', []]] = 'baz';
+    $array[['foo', []]] = 'qux';
+
+    var_dump($array->toArray());
+
+    // => array(2) {
+    //    ["foo"]=>
+    //        array(2) {
+    //            [0]=>
+    //                string(3) "baz"
+    //            [1]=>
+    //                string(3) "qux"
+    //        }
+    //    [0]=>
+    //        string(3) "bar"
+    // }
+
+```
+
+### 4. offsetUnset:
+
+You can unset nested key.
+
+```php
+    $array = new CompositeKeyArray([
+        'foo' => [
+            'bar' => 'baz'
+        ]
+    ]);
+
+    unset($array[['foo', 'bar']]);
+
+    var_dump($array['foo']); // => array(0) {}
+```
+
+After nested manipulations you might want to get back the **real array**. This can be done by calling `$array->toArray()`.