Make aiohttp dependency optional

[pirogoeth]

Includes:

• Documentation update calling out the aiohttp extra for both the Service and Pusher features
• Import guards in pusher and service
• Runtime checks in the Pusher and Service initializers, to retain consistency in the top-level API
• Quoted type annotations where aiohttp.web.* might not be available
• Version bump to 19.11.0

---

@claws let me know if there is anything I missed or if you have any concerns, thanks! :)

[claws]

Looks mostly there. A few things...

Could you run the dev guide (in docs/dev/index.rst) on your beanch to confirm they still work as written? Specifically:

• Please run make style to ensure style compliance. I really do need to add this step to the CI suite.

• I think the make test step will fail because at least one unit test expects that aiohttp is installed. This could be resolved by changing the install instruction from pip install -e . to pip install -e .[aiohttp] or wrapping the unit tests that need aiohttp with a @unittest.skipUnless(...) check similar to that used in the tests/test_quart.py file. I prefer the first option.

• Don't worry about the make check_types step failing - it does not work in master either. I have not been able to get that to work cleanly yet.

[pirogoeth]

@claws Do you think it would be reasonable to have the pip install -r requirements.dev.txt install the complete development environment by including -e .[aiohttp] in the requirements.dev.txt itself?

I've added a commit which introduces the above. If you don't like it, I've no qualms reverting and adjusting the documentation accordingly :)

[claws]

I have push a new release of aioprometheus (19.11.0) to PyPI which contains your changes.