Python 3 11 support

[rpsteiger]

Hello, I spent some time to make this project work with current Python version 3.11.

It should work out of the box, like so:

python3 -m venv .
source bin/activate
pip3 install -r requirements
python3 app.py

or using Docker, like so:

docker build -t aoe2-api:v1 .
docker run --rm -d -p 8080:8080 aoe2-api:v1

I changed the Dockerfile to use gunicorn, since I think this is the easiest solution that works well in a production environment.

Tested to work in Python3.11. The unit tests also work.

[rpsteiger]

@aalises If you are happy with it, you can merge it. I don't have the rights necessary :)