Python 391 support

[kuzeyron]

With these changes Python 3.9.1 should be able to run on your devices.

In order to run 3.9.1 on your device:
requirements = python3==3.9.1,hostpython3==3.9.1,kivy==master,setuptools==51.1.1,cython==0.29.21

My example code to run:

import platform
from kivy.app import App
from kivy.uix.button import Button

class TestApp(App):

    def build(self):
        return Button(
            text=f'hello world - {platform.python_version()}')

if __name__ == '__main__':
    TestApp().run()

[obfusk]

There was already a PR for that: #2337 :)

[kuzeyron]

There was already a PR for that: #2337 :)

Obviously your PR is going to step on a few land mines. At least for those who is running 3.9.1 on their systems.

[obfusk]

#2394 has been merged :)

[misl6]

Superseded by #2394.