The recent `flake8==3.8.1` update reported new errors:
```
kivy_ios/toolchain.py:292:31: E741 ambiguous variable name 'l'
...
```
Also note the entire `xcassets.py` file is being ignored as we can't
seem to use one ignore for the entire list anymore. I'm not sure if
this is a regression or a new feature from flake8.
- updates all imports to prefix kivy_ios
- adds basic `setup.py` file
- adds a simple `toolchain.py` to the root folder for compat
Makes it possible to install kivy-ios from PyPI:
```
pip install kivy-ios
toolchain --help
```
Note the `rebuild_updated_recipes.py` is expected to fail as we
moved all the recipes.
This is a working, but unperfect iteration that come with limitations
we would address in subsequent pull requests, such as:
- the new usage is not yet documented
- CI is not testing the source distribution creation and install
- Continuous Delivery to PyPI is not in place
- `toolchain` binary is a bit too generic name
- we're still vendoring things under `tools/`
