Add the "Framework :: AnyIO" classifier

[uSpike]

Request to add a new Trove classifier.

The name of the classifier(s) you would like to add:

• "Framework :: AnyIO"

Why do you want to add this classifier?

AnyIO is an asynchronous networking and concurrency library that works on top of either asyncio or trio. It is the basis for at least 96 projects on PyPI, including starlette and (soon) FastAPI. Currently the available relevant classifiers are "Framework :: AsyncIO" and "Framework :: Trio", and searching for the combination of these classifiers results in 56 matching projects. In the future, AnyIO may support additional back-ends which would complicate the classifiers further. Many existing projects (such as anyio-mqtt or anyio-serial name themselves specifically to increase discoverability. A specific PyPI classifier would improve the discoverability of these projects for the long-term future.

Closes #11

[uSpike]

FastAPI has released https://github.com/tiangolo/fastapi/releases/tag/0.70.0 and https://github.com/tiangolo/fastapi/releases/tag/0.69.0 which require Anyio, and the number of libraries dependent on Anyio has grown to 102.

[uSpike]

anyio now has 131 dependent packages on PyPI. Framework :: AsyncIO + Framework :: Trio results in 12 projects. It would be very nice to have this new classifier!