Support __self__ on asynq'ed methods

[besfahbod]

Regular PY bound method objects have a __self__ attribute, pointing to the object they are bound to.

Would be great to be able to have the same for asynq()ed methods.

In [36]: class A:
    ...:     def foo():
    ...:         pass
    ...:     @asynq()
    ...:     def bar():
    ...:         pass
    ...:

In [37]: A().foo.__self__.__class__ is A
Out[37]: True

In [38]: A().bar.__self__.__class__ is A

Traceback (most recent call last):
  File "/.../venv/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 2862, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-38-a140d1d32042>", line 1, in <module>
    A().bar.__self__.__class__ is A
AttributeError: 'asynq.decorators.AsyncDecoratorBinder' object has no attribute '__self__'
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-38-a140d1d32042> in <module>()
----> 1 A().bar.__self__.__class__ is A

AttributeError: 'asynq.decorators.AsyncDecoratorBinder' object has no attribute '__self__'

[JelleZijlstra]

You can currently already do this with .instance; I agree that it would be more consistent to support __self__ though. I submitted quora/qcore#70 to fix this.

[besfahbod]

Uh, I didn't find `.instance' when trying things out in ipython. Thanks for both! :)