Bump version to 0.9.0

[kngwyu]

Resolves #808

[birkenfeld]

@kngwyu I'd like to update the docstrings of pyo3 types to point to the new guide first. I can do it today.

[kngwyu]

@birkenfeld
Thank you!
I'm willing to wait for that.

[birkenfeld]

Can we also import PyAny to the main crate namespace?

[kngwyu]

@birkenfeld
I don't have any strong opinions about that.
They are hidden since 302c099 and left as is.
@konstin
What kind of intention did you have for not exposing types::* in lib.rs?

[birkenfeld]

I think it makes sense to put the long list of concrete types there.

But if we want to enhance visibility of PyAny and make clear that it's an important type, counterpart to PyObject, it should be in the root/prelude.

[konstin]

The idea was to prevent the top level from becoming to cluttered with all the builtin types. But imo PyAny can also be the root namespace and/or the prelude.

[kngwyu]

@birkenfeld @konstin
Thank you for the feedback!
I'll create a PR for PyAny later.

[kngwyu]

Now ready to release :)

[birkenfeld]

Thanks! Can you set a tag?

[kngwyu]

Sure, I made it now. https://github.com/PyO3/pyo3/releases/tag/v0.9.0