Injectable

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* Support for optional injection in declarative fashion: ``Autowired(Optional[...])``

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* Fix ``Autowired(List[...])`` not working with qualifiers

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* Fix Windows injectables not being loaded.

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* Remove unused ``inspect`` imports.

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* Fix bug of scanning the same module more than once when ``InjectionContainer.load()``
is called multiple times with different relative search paths.

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* Added ``injectable_factory`` decorator for declaring injectable factory methods
* Include the console output in the examples