Create requests-async based TestClient, remove aiohttp dependency, drop Python 3.5

Update all tests to be compatible with requests-async
Cleanup testing client changes with black and isort
Remove Python 3.5 and other meta doc cleanup
rename pyproject and fix pep517 error
Add black config to tox.ini
Cleanup tests and remove aiohttp
tox.ini change for easier development commands
Remove aiohttp from changelog and requirements
Cleanup imports and Makefile

tests/performance/bottle/simple_server.py

@@ -1,8 +1,9 @@
 # Run with: gunicorn --workers=1 --worker-class=meinheld.gmeinheld.MeinheldWorker -b :8000 simple_server:app
 import bottle
-from bottle import route, run
 import ujson
 
+from bottle import route, run
+
 
 @route("/")
 def index():