Payplug

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- Add missing `Billing` and `Shipping` entities to payment resource

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- Add AccountingReport class to handle the new /accounting\_reports API endpoint

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- Add API version setting
- Fix tests
- Move CI to Github Actions

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- Require pyOpenSSL>=0.15 to prevent random failures.
- Log more errors in case of request failure.

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- **NEW**: Support for Customers and Cards. (see official documentation)
- **NEW**: Add ability to abort payment objects.


payment.abort()


- **NEW**: This library is now under MIT Licence (Issue 4).
- Minor fixes in tests.
- Add this changelog.