Sorry, but what changelog are you talking about?
Mibew Messenger 2.0 is not released yet. We have
our roadmap. Some things from that roadmap will be available in version 2.0, some will be implemented in later versions. (For example, Plugins API is already there, though it's not finalized yet.)
In the repository you can see the history of commits to figure out what we've done and what we're working over at present time. But we will not prepare a special document describing all differences between Mibew 1.6.x and Mibew 2.x and update it after each new commit.
p.s. I've moved your post into a separate topic. Separate questions should be asked in separate topics.