Zbarcam

- Bumps dependencies versions, refs 31

- Setup coverage testing
- Bump to `xcamera>=2019.928`
- Continuous integration improvements

- Use new `xcamera` from PyPI
- Use `opencv-python` from PyPI, refs 23

- Fix camera events not binded
- Makefile improvements
- Bump to Kivy==1.11.1, refs 22

- Update buildozer, p4a, and ndk versions, refs 21
- Publish to F-Droid, refs 20
- Improve Android camera permission handling, refs 12, 16
- Use upstream autofocus, refs 8

- Update Cython for Python3.7 support, refs 35
- Make garden.zbarcam a package again, refs 36
- Don't ship opencv directory to APK, refs 37
- Migrate to new garden structure, refs 17
- Publish documentation to readthedocs, refs 18
- Publish to PyPI, refs 19