This is a major rewrite, so there are a lot of cool changes like much better performance, better ts support, separating the underlying parts of vue to do things

This is a major rewrite, so there are a lot of cool changes like much better performance, better ts support, separating the underlying parts of vue to do things like have better control of making things reactive, then the api change that everyone has been panicking about, use of proxies (the implications of which I can't remember now), etc.