[WIP] Third-party modules

Trying to use well-tested third-party modules instead of private clones.

Searching for modules that works with

- Node.js
- Browser
- (Hopefully) AMD

Then, test them on browser/AMD too!

TODO
----------
- [x] Migrate `traverse` function to `estraverse` module
- [x] Test and CI under browser
- [x] Test and CI under AMD
- [x] Refactoring (reduce complexity!)