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

docs/sanic/changelog.md

@@ -1,3 +1,18 @@
+Version 19.6
+------------
+19.6.0
+  - Changes:
+    - Remove `aiohttp` dependencey and create new `SanicTestClient` based upon
+    [`requests-async`](https://github.com/encode/requests-async).
+
+  - Deprecation:
+    - Support for Python 3.5
+
+Note: Sanic will not support Python 3.5 from version 19.6 and forward. However,
+version 18.12LTS will have its support period extended thru December 2020, and
+therefore passing Python's official support version 3.5, which is set to expire
+in September 2020.
+
 Version 19.3
 -------------
 19.3.1

docs/sanic/testing.md

@@ -1,8 +1,8 @@
 # Testing
 
 Sanic endpoints can be tested locally using the `test_client` object, which
-depends on the additional [aiohttp](https://aiohttp.readthedocs.io/en/stable/)
-library. 
+depends on the additional [`requests-async`](https://github.com/encode/requests-async)
+library, which implements an API that mirrors the `requests` library.
 
 The `test_client` exposes `get`, `post`, `put`, `delete`, `patch`, `head` and `options` methods
 for you to run against your application. A simple example (using pytest) is like follows:
@@ -21,7 +21,7 @@ def test_index_put_not_allowed():
 ```
 
 Internally, each time you call one of the `test_client` methods, the Sanic app is run at `127.0.0.1:42101` and 
-your test request is executed against your application, using `aiohttp`. 
+your test request is executed against your application, using `requests-async`. 
 
 The `test_client` methods accept the following arguments and keyword arguments:
 
@@ -33,7 +33,7 @@ The `test_client` methods accept the following arguments and keyword arguments:
 - `server_kwargs` *(default `{}`) a dict of additional arguments to pass into `app.run` before the test request is run.
 - `debug` *(default `False`)* A boolean which determines whether to run the server in debug mode.
 
-The function further takes the `*request_args` and `**request_kwargs`, which are passed directly to the aiohttp ClientSession request.
+The function further takes the `*request_args` and `**request_kwargs`, which are passed directly to the request.
 
 For example, to supply data to a GET request, you would do the following:
 
@@ -55,8 +55,8 @@ def test_post_json_request_includes_data():
 
 
 More information about
-the available arguments to aiohttp can be found
-[in the documentation for ClientSession](https://aiohttp.readthedocs.io/en/stable/client_reference.html#client-session).
+the available arguments to `requests-async` can be found
+[in the documentation for `requests`](https://2.python-requests.org/en/master/).
 
 
 ## Using a random port