Acknowledge support

[hvaddi9]

Description

Please describe your pull request.

Supports In-App Purchase or Subscription Acknowledgement. If user provides an extra parameter developerPayload (the body parameter in acknowledge method), it acknowledges the purchase.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Documentation:

• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

[hvaddi9]

I also feel that there's lot of redundant code in verifyINAPP & verifySub functions. URI is only value that changes between them. Hence, they can be combined together. But I assume, a lot of existing users must be using these functions separately.

[Deishelon]

Hey, looks good👍 Will update documentation to reflect changes and will push the update to npm

Will clean up duplicated code in the future release :)