Create Babel parser/transform plugins for proposals in TC39

As a part of my project, I'll take ownership of object rest spread, transform decorators, optional chaining, private fields, and async-await specifications and keep them updated, spec-compliant, tested and bug-free.

I am a JavaScript developer and I'm really excited about what Babel does. Babel allows everyone to have access to future language features which make life easier, code cleaner, and give devs one less thing to worry about upgrading in next few months. As a side-note, I love things that compile to JavaScript, and I'm really excited about what I'll learn (AST manipulation, details of the JavaScript AST, lexing & parsing) as a part of my work on Babel.