HACKING is rst file
get_attribute fixes

- get_attribute and __getattribute__ (new) raise AttributeError so data descriptor lookup must be protected with try/except
- don't forget to look attribute as javascript attributes in _get_upstream_attribute because base object have no __dict__
pys: missing handling of variable scope in orelse blocks
pys: actual fix for variable scoping of variable defined in else block
remove wild debug statment
runtime: new class definition & method call is working
missing unit tests
update HACKING.rst