Inline type hints

[Daverball]

Hi, I wrote some third party stubs for WebTest for something I was working on and was wondering if there is any interest in merging them into the code base.

I previously wrote stubs for WebOb and contributed them to typeshed and have an open PR to get those merged into the WebOb code base.

I am willing to do the same for WebTest. I do already have a PR open on typeshed for those stubs. But if you're willing to add inline type hints, then it makes more sense to do that, rather than publish a third party stubs package that's going to be obsolete within a short few weeks.