Add Framework :: aiohttp classifier

[asvetlov]

Request to add a new Trove classifier.

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

• Framework :: aiohttp

Why do you want to add this classifier?

https://github.com/aio-libs/aiohttp is very widely used in the Python community.
It has 13M downloads per month at the moment of writing: https://pypistats.org/packages/aiohttp
More than 50 libraries officially claim that they are built on top of aiohttp: https://docs.aiohttp.org/en/stable/third_party.html
Many more libraries exist but out of the list.
libraries.io claims that 1141 PyPI packages depend on aiohttp: https://libraries.io/pypi/aiohttp/dependents

Adding a trove classifier would benefit the project as it will make related projects more discoverable.
aiohttp already has a big and stable ecosystem, adding a dedicated classifier simplifies the searching.

Fixes #54

[webknjaz]

@asvetlov this needs a conflict resolution.

@di is it possible to expedite the merge?