Reflection element serialization

This pull request makes reflective elements serializable. This way, for example, the REST API can be extended to cache results from ist DefaultRouter using `serialize()` and `unserialize()` - in a real-life test scenario, this more than tripled the speed of routing setup.

### Before
```sh
$ xp -w 'unserialize(serialize(XPClass::forName("lang.Object")->getMethod("equals")))'
Exception lang.Error (Fatal error: ReflectionMethod::getDeclaringClass(): Internal error: Failed
  to retrieve the reflection object in F:\...\lang\reflect\Routine.class.php on line 290)
  at <main>::__output((0xdf)'', 9) [line 0 of StackTraceElement.class.php]
```

### After
```sh
$ xp -w 'unserialize(serialize(XPClass::forName("lang.Object")->getMethod("equals")))'
public bool equals(lang.Generic $cmp)
```