Support for raw chinese_whispers

This commit introduces chinese_whispers method without any "helpers" on
PHP side. Users needs to take care of everything (building edges from
128D face chip vector, for example), but this is exposed for people
that need low-level call and want to calculate distances and build edges
in PHP directly.

README.md

@@ -71,9 +71,28 @@ var_dump($landmarks);
 
 ```
 
+#### chinese whisers
+
+Provides raw access to dlib's `chinese_whispers` function.
+Client need to build and provide edges. Edges are provided
+as numeric array. Each element of this array should also be
+numeric array with 2 elements of long type.
+
+Returned value is also numeric array, containing obtained labels.
+
+```php
+<?php
+// This example will cluster nodes 0 and 1, but would leave 2 out.
+// $labels will look like [0,0,1].
+$edges = [[0,0], [0,1], [1,1], [2,2]];
+$labels = dlib_chinese_whispers($edges);
+
+```
+
 ## Features
 - [x] 1.Face Detection
 - [x] 2.Face Landmark Detection
 - [ ] 3.Deep Face Recognition
 - [x] 4.Deep Learning Face Detection
+- [x] 5. Raw chinese_whispers