added support for __call() in expression resolution (closes #2)

The new algorithm for object method resolution is now the following:

  * get all methods declared for `$object` using ReflectionObject::getMethods()
  * check if `$item` is in the list of method names
  * check if `get$item` is in the list of method names
  * check if `__call` is defined and pass `$item` as the method name

test/fixtures/expressions/magic_call.test

@@ -0,0 +1,27 @@
+--TEST--
+Twig supports __call() for attributes
+--TEMPLATE--
+{{ foo.foo }}
+{{ foo.bar }}
+--DATA--
+class TestClassForMagicCallAttributes
+{
+  public function getBar()
+  {
+    return 'bar_from_getbar';
+  }
+
+  public function __call($method, $arguments)
+  {
+    if ('foo' === $method)
+    {
+      return 'foo_from_call';
+    }
+
+    return false;
+  }
+}
+return array('foo' => new TestClassForMagicCallAttributes())
+--EXPECT--
+foo_from_call
+bar_from_getbar