Add @Result annotation for @OnActivityResult

This PR is implementing #796 which I really wanted to be implemented
``@Result`` is added to retrieve the values from intent

```java
    Bundle extras_ = (((data == null)||(data.getExtras() == null))?new Bundle():data.getExtras());
    switch (requestCode) {
        case  44 :
            {
                int value_ = extras_.getInt("value");
                String s_ = extras_.getString("s");
                Uri uri_ = extras_.getParcelable("uri");
                ArrayList<Uri> uris_ = extras_.getParcelableArrayList("uris");
                String[] strings_ = extras_.getStringArray("strings");
                AwaitingResultActivity_.this.onResultWithResultExtra(resultCode, value_, s_, uri_, uris_, strings_);
            }
            break;
    ......
```
this is a snippet from a generated code.
``extras_`` was newly declared and one block was added for variable's scope
Please, add some javadoc on the annotation. See existing annotations to have some examples.