Make app creating factory async

[gyermolenko]

To be able to run application with gunicorn I made the application creating factory async (fix #10).
Unfortunately I got unrecognized arguments error from

gunicorn aiohttpdemo_polls.main:init_app --bind localhost:8080 --worker-class aiohttp.GunicornWebWorker

so I've also substituted parse_args with parse_known_args as a workaround:

# ignore unknown options
options, unknown = ap.parse_known_args(argv)

Please review get_config function usages and parts of logic related to usage of argv and get_config(['-c', USER_CONFIG_PATH.as_posix()]). It looks ugly but I can't find a better way (if we still want command line args).

[f6m6]

As soon as the tests pass let's merge this!

[jettify]

what about other demos? any plan to make factories there?

[webknjaz]

It seems to me that you re-implement what's available in https://pypi.org/project/aio_manager/ (manage.py / argparse wrapper, might be overkill for now) + https://pypi.org/project/aio_yamlconfig/ (reads yaml config, checks it against trafaret schema, saves to app.config), is it your intention to avoid external dependencies?

[gyermolenko]

@webknjaz
I don't avoid external dependencies. aio_manager looks like an overkill, but aio_yamlconfig can probably fit. Although I was thinking about yamllint. Need some opinions from others.

We have at least 3 kinds of app start:

1. python main.py
2. tests
3. gunicorn

So if we want flexible app configuration - what are best practices here?
Current implementation is to pass -c ./path/to/config_file.xxx from command line for start option 1... and 2 workarounds (for start options 2 and 3).

[gyermolenko]

@jettify

what about other demos? any plan to make factories there?

I can do that, sure. Do we want other similarities between different demos?

[webknjaz]

I'd say priority for config lookup should follow unix-way:

1. passed as CLI arg (-c, --config)

   1.1. (maybe) $PWD/config/app_config_name.yaml

2. ~/.app_config_name.yaml

3. /etc/app_config_name.yaml

[jettify]

@gyermolenko not sure but essential parts should be the same I think like factories, new APIs

[jettify]

@webknjaz would you like submit PR with your suggestion?

[jettify]

Feel free to merge. Other improvements could be done in separate PRs

[webknjaz]

@jettify i'll do if i have time