1.2.15

In this release we have added a new method that provides a completion handler for renewing an authentication token.
We also updated the documentation to clarify the thread policy for public method callbacks.

• A new renewAuth method was added to Auth and the renew method was deprecated

Implemented enhancements:

• Add new renew async method #816 (ikbalkaya)

Fixed bugs:

• Early return from onAuthUpdated creates issues #814

Closed issues:

• Invalid method implementation in README #819
• Document which thread is whole SDK or callbacks using #800

Merged pull requests:

• Update onChannelStateChanged readme with current implementation #820 (qsdigor)
• Document thread policy for callbacks and add missing documentation for callbacks #818 (qsdigor)