Wai-common

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- Added load_dir function to file package, which can load all files in a directory.

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- Removed restriction that switch only work with enums. Now can switch on any type.
Onus is on the user to handle modifications of the switched value during switching.
- Added **abc** package, with utilities for working with abstract classes/methods.
- Added **decorator** package, with custom decorators.

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- Initial release