Cleanup application construction

[netomi]

This PR does the following changes:

• removes hack wrt hypercorn and __file__ parameter. Also hypercorn now only loads the application in the worker process, see Only load the application in the main process if the reloader is being used. pgjones/hypercorn#143
• update simple example app
• add Makefile to showcase how the example app can be started in development and ASGI mode
• update README

[netomi]

I kept app.cfg around for the time being. If you dont like the idea with the ASFQuartConfig its fine by me.
It just was a bit confusing to have 2 different configs, and you need to think which one to access.

[netomi]

to get a better understanding of the reason for the PR:

we certainly want to use hypercorn to run our applications in production mode and do not want to have any development settings active in such a mode, e.g. reload of the application in case of source or config file changes.

Also we at least want to have the option to use multiple workers for the app, and in such a case, using an ASGI server directly is the only option.

runx is great for development, so that the app restarts itself when something changes, or templates are refreshed. However, for a production service this is not what you want in any case.

I made this distinction also in the README and added a Makefile to showcase how you can run the app in both modes.

[dave2wave]

@netomi Any changes needed to the docs?

[netomi]

I did a small update on the docs, but my changes did not touch anything that is described there.