Ping-sdk

- The SDK has been updated to support all endpoints of payments API.

- update_payment_order() now working.

- Requirements for which python versions are compatible with the SDKt have been updated and checked.

- The SDK is compatible Python 3 versions 3.7 and later.

- Tests to ensure that the SDK works on several operating systems have been implemented.
- The tests include: Ubuntu, Windows and Mac OS.

An SDK update to support new API changes regarding the initialization of a payment.

- Added `payment_iq` as a new provider when initiating a payment

An SDK update to support new API changes regarding initialization of a payment.

- Each order item now requires a merchant id
- Unit-Tests updated to support this change
- Documentation updated to support this change

- The SDK have been updated to support the whole payments API.