Support flask 2
Flask 2 works *almost* out of the box, however it breaks `example_data.py`, see below:
---
When running example_data.py, the following error appears:
[error-example-data.txt](/uploads/04e1c218f4eb96b25e461fadae5f3e3e/error-example-data.txt)
The print message:
```
<WrapperTestResponse streamed [400 BAD REQUEST]>
```
is from adding print(generated) in line 381 of example_data.py
It seems like the error takes place when parsing the arguments in line 406 of exams.py
(removing the 'add arguments' and assigning values manually in exams.py gives no errors.)
issue