Add aspect reflection class

[Matthimatiker]

Create an aspect reflection class that provides simplified access to aspect specific components like pointcuts and advices.

Use the new reflection class to refactor the AspectPHP_Advice_Extractor class.

[Matthimatiker]

The class AspectPHP_Reflection_Aspect may be used to inspect aspects.
Used the new reflection class to refactor the code that extracts advisors.