Request for feedback: `destructor` macro

[Araq]

If you use Nim's `ref` you should stick to Nim's ARC/ORC thing. Upcoming 
version 2.2 got some better support to track down cycle leaks. It is usually a 
bad idea to interfer with the compiler in ways unforseen by the compiler devs 
;-), if you want your own memory management you should use `ptr`.