Updates and fixes, working in Python 3.10

[tachylatus]

This PR includes changes from other forks.

Changes introduced by tachylatus fork:

• Rework requirements.txt
• Fix indentation error
• Support both 2-tuple and 3-tuple output from cv2.findContours

Tested and working in Python 3.10.0.

Setup:

python -m venv venv310
pip install -r requirements.txt
python page_dewarp.py ./example_input/boston_cooking_a.jpg

[sergiocorreia]

Hi @tachylatus ,

Assuming Matt doesn't have the bandwidth to maintain this repo, would you be willing to maintain a canonical fork that others can point to, and contribute to?