What is 4.0.0?

[steveRoll-git]

I'm noticing that sumneko is still actively working on the 4.0.0 branch. However it's not documented how this new version will be different, or what it improves on. All the commit messages are in Chinese so as a non-speaker I can't infer what is being worked on.

If you're willing to share, @sumneko, I am curious to know what this new version is.