It is a long overdue update with minor changes. The only reason it is labelled 2.1.0 and not 2.0.3 is because the minimum supported version is 5.0.1 instead of 5.0.0 (Unity has a fix for WebGL builds).

Another big thing obviously is that the licence changed from GPLv2 to MIT. Indeed, I wasn’t aware that with the former, if you wanted to include this Unity API in your project, it would force you to release the source code of your game as well. Oops.
Thanks to Milho and r2d2rigo for their input.

Last but not least, I use to work for a video-game company which was preventing me from releasing this to the Unity Asset Store but this is no longer the case. While I can’t give you a release date for now, I’ll be working on making it happen.

Warning:

• The minimum version to use the API is now Unity 5.0.1.

• License is now MIT (less restrictive).

Fix:

• ShowLeaderboards callback not being called. Thanks to @michidk for his contribution and @WizzardMaker for his help.

• Call signature could be invalid when using URL with forward slash. Thanks to DerpVulpes for his contribution

Thanks all for using the API, for your feedback and bug reports.

Also thanks to @andyman for helping other users on Twitter. When I couldn’t answer (probably sleeping because of timezone difference), he was really helpful to the community.