Update Changelog for 0.15 & present

I did my best to get all this together -- it's kind of a mix of commits & PRs, but I think I got the main stuff. Is it passable?

@batmanjs/owners , I know a lot of you guys are on other projects now, but I gotta say :sparkles: __THANK YOU__ :heart: for all your amazing work! Batman.js is a joy to use and it makes my job really enjoyable. It's always impressive to look back at all that you've done to make it a great framework!