Pylibmagic

This release supersedes v0.1.0, by now shipping the `magic.mgc` file.
- `ctypes.CDLL` is patched to handle the situations for `sys.platform == 'linux'` where `ctypes.util.find_library` does not return an absoluate path, but also because `python-magic` hardcodes the libname as `libmagic.so.1`
- make sure we are able to test the package by adding a test to make sure the GitHub Action runners properly fail upon `import magic` (see `tests/test_import.py`)

First stable release published to pypi.
- README is migrated to rst to include in the RTD docs as well

Core functionality support for linux and mac:
- tests are running for linux and mac
- windows tests are marked as allowed to fail
- wheels are built for linux and mac
- wheels are not built for windows

This release will be manually uploaded to test.pypi to test the functionality there first.