ASGI

As discussed in #1979, the current CONTRIBUTING.md document instructs people to run tools/mintest.sh, which requires Python 3.8 and 3.5 installed simultaneously and then it makes things a bit confusing when referencing Python 3.6 or 3.7 and then pyenv shell 3.8.0 3.5.8 and then further below pyenv virtualenv 3.8.0 falcon-sandbox-38. I'm not familiar with pyenv, but this

With the recent bug-fix in #1463, I noticed a lack of tests directly testing UnionDefinition.get_type_resolver and the function that it returns. We should add these.

Should add a section to the docs for third-party examples and guides using Mangum

It would be nice if there was a new clause which can be added to queries called callback.

For example:

def callback_handler(success, value):
    if success:
        print(f'The query was successful and returned {value}')
    else:
        print("The query failed")

Band.select().callback(callback_handler).run_sync()

The callback could be a function or coroutine, wh