Apipkg

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* restore tox.ini to support tox --current-env based packaging

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* add support for python 3.11 and drop dead pythons (thanks hukgo)
* migrate to hatch
* split up __init__.py
* add some type annotations

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* drop the python 3.4 support marker, 2.1.0 broke it

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- fix race condition for import of modules using apipkg.initpkg in Python 3.3+
by updating existing modules in-place rather than replacing in sys.modules
with an apipkg.ApiModule instances. This race condition exists for
import statements (and __import__) in Python 3.3+ where sys.modules is
checked before obtaining an import lock, and for importlib.import_module
in Python 3.11+ for the same reason.

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- fix race conditions for attribute creation

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- also transfer __spec__ attribute
- make py.test hack more specific to avoid hiding real errors
- switch from Travis CI to GitHub Actions
- modernize package build
- reformat code with black