Async-support-fastapi-sample

[ninyawee]

create for #340 to add fastapi sample

[CLAassistant]

All committers have signed the CLA.

[clsung]

Some files (i.e. aiohttp_async_http_client.py, async_api.py) are already committed in #340?

[ninyawee]

Some files (i.e. aiohttp_async_http_client.py, async_api.py) are already committed in #340?

I reseted and added changes on top of master.

[ninyawee]

could you add this as a part of hacktoberfest. more info here

[louis70109]

LGTM

[i-Ching]

I replace aiohttp.ClientSession() with httpx.AsyncClient(), it works.
Hence I don't need import aiohttp under FastAPI or starlette environment.

import httpx
session = httpx.AsyncClient()
async_http_client = AiohttpAsyncHttpClient(session)
...