Allow calling Py::as_ref() and Py::into_ref() against PySequence, PyIterator and PyMapping.

[moriyoshi]

This patch allows one to call Py::as_ref() against PySequence by supplying PyTypeInfo for it.

[davidhewitt]

Sorry for being AWOL the past week, I've been swamped and not able to keep up with OSS. This is top of my list to review either tonight or tomorrow evening.

[davidhewitt]

Thanks, overall I'm in favour of having these two APIs for Py<PySequence>. I think it's perfectly fine to add these in manually. Maybe in the future we'll have a trait which automatically produces this API again.

If it's not too much to ask, would you be willing to add the same for Py<PyIterator>, which is in almost exactly the same position?

[moriyoshi]

If it's not too much to ask, would you be willing to add the same for Py, which is in almost exactly the same position?

That's also what I've been wondering. Sounds nice.

[moriyoshi]

I think I've done with them. Can you take a look?

[davidhewitt]

Thanks, it's looking almost there!

There's a new implementation for IntoPyPointer for PyAny which isn't sound and needs to be removed.

Also I made a few comments to tidy up the tests a little bit.

Finally, looks like you may need to run cargo fmt before you repush.

[davidhewitt]

I'm going to finish this up and also add support for PyMapping; will push onto this branch. Thanks for getting it to this point.