Make register()/unregister() in subclasses return a _Key.
Make register()/unregister() in subclasses return a _Key.

fallen/asyncio,1st1/asyncio,manipopopo/asyncio,1st1/asyncio,haypo/trollius,fallen/asyncio,vxgmichel/asyncio,manipopopo/asyncio,gvanrossum/asyncio,gsb-eng/asyncio,gvanrossum/asyncio,gvanrossum/asyncio,jashandeep-sohi/asyncio,haypo/trollius,vxgmichel/asyncio,manipopopo/asyncio,haypo/trollius,jashandeep-sohi/asyncio,fallen/asyncio,ajdavis/asyncio,ajdavis/asyncio,gsb-eng/asyncio,Martiusweb/asyncio,vxgmichel/asyncio,1st1/asyncio,gsb-eng/asyncio,ajdavis/asyncio,Martiusweb/asyncio,Martiusweb/asyncio,jashandeep-sohi/asyncio