README: add link to rock-dev thread
add "extractor2" -- sorry for bad name...

this one uses the recursive-ast-visitor instead of ast_matchers

still, the thing is slow as a slug... (actually "exactly" as fast as the "extractor")

note: this has no fancy record-layout-output... this would be a copy-n-paste from the other one...

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>