Drops system, host and target Python 2 support.
Note a lot of recipes were having hardcoded reference to
`lib/python2.7/site-packages/` directory. I suspect most
of theses were not working, but the reference has been updated
to `lib/python3.7/site-packages/` following the same hardcoding
pattern. In follow up work we would do a walkthrough each recipes
to fix at least compilation time issues.
Also note the `rebuild_updated_recipes.py` is expected to fail as
this is touching many recipes including recipes that were already
broken.
- 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/`
