Merge branch '1.x' into 2.x

* 1.x:
  added the key to the map and filter filters
  added support for iterators
  removed fn in front of arrow functions
  changed arrow syntax
  added "filter", "map", and "reduce" filters
  simplified code
  fixed CS
  fixed partial output leak when a PHP fatal error occurs

src/Node/SetNode.php

@@ -58,7 +58,7 @@ class SetNode extends Node implements NodeCaptureInterface
         } else {
             if ($this->getAttribute('capture')) {
                 $compiler
-                    ->write("ob_start();\n")
+                    ->write("ob_start(function () { return ''; });\n")
                     ->subcompile($this->getNode('values'))
                 ;
             }