.a.b.c notation for nested attrgetter

[ghost]

obj |> .a.b.c
# currently does:
obj |> attrgetter('a').b.c  # error!
# would be neat if it did:
obj |> attrgetter('a.b.c')  # more expected imo!

[evhub]

@Socialery That's a great catch; I'll implement in the next version for sure. Thanks!

[evhub]

@Socialery This now works in coconut-develop! Just pip install coconut-develop to get the new behaviour.