Added forkTo and forkFrom methods

Author: Matt Humphrey

lib/Gitlab/Api/Projects.php

@@ -148,4 +148,14 @@ public function search($query)
         return $this->get('projects/search/'.urlencode($query));
     }
 
+    public function createForkRelation($project_id, $forked_project_id)
+    {
+        return $this->post('projects/'.urlencode($project_id).'/fork/'.urlencode($forked_project_id));
+    }
+
+    public function removeForkRelation($project_id)
+    {
+        return $this->delete('projects/'.urlencode($project_id).'/fork');
+    }
+
 }

lib/Gitlab/Model/Project.php

@@ -496,4 +496,24 @@ public function transfer($group_id)
 
 		return $group->transfer($this->id);
 	}
+
+    public function forkTo($id)
+    {
+        return $this->api('projects')->createForkRelation($id, $this->id);
+    }
+
+    public function forkFrom($id)
+    {
+        return $this->createForkRelation($id);
+    }
+
+    public function createForkRelation($id)
+    {
+        return $this->api('projects')->createForkRelation($this->id, $id);
+    }
+
+    public function removeForkRelation()
+    {
+        return $this->api('projects')->removeForkRelation($this->id);
+    }
 }