Add an experimental suffix to the new features (also mark them deprecated and...

Add an experimental suffix to the new features (also mark them deprecated and show a big warning in the Javadoc). Revert to ASM6 for the default api of the visitors, and use ASM7_EXPERIMENTAL only in tests (only exception: Trace*Visitor classes, which are final). This pattern could allow us to develop any new feature directly in 'master'.