Since we are going to move more pygolang functionality into C++ (timers,
context, ...), and since C++ does not have garbage collector, we will
need to find a way to automatically manage memory in leak/error free way.

Let's do this via refptr<T> smart pointer (inspired by WebKit's RefPtr<T>),
which, similarly to chan<T> automatically manages pointed object's
lifetime through reference counting.

refptr<T> will be used in follow-up patches.

Top-level documentation is TODO.