Import-linter

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* Officially support Python 3.11.

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* Include py.typed file in package data to support type checking
* Remove upper bounds on dependencies. This allows usage of Grimp 2.0, which should significantly speed up checking of
layers contracts.
* Add --verbose flag to lint-imports command.
* Improve algorithm for independence contracts, in the following ways:
- It is significantly faster.
- As with layers contracts, reports of illegal indirect imports reports now include multiple start
and end points (if they exist).
- Illegal indirect imports that are via other modules listed in the contract are no longer listed.

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* Add Python API for reading configuration.
* Add support for namespace packages.

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* Officially support Python 3.10.
* Drop support for Python 3.6.
* Add support for default Field values.
* Add EnumField.
* Support warnings in contract checks.
* Add unmatched_ignore_imports_alerting option for each contract.
* Add command line argument for showing timings.

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* Fix bug with ignoring external imports that occur multiple times in the same module.

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* Wildcard support for ignored imports.
* Convert TOML booleans to strings in UserOptions, to make consistent with INI file parsing.