refactor jsdoc.js; update Rhino

- Switched to a new Rhino fork: https://github.com/jsdoc3/rhino
  (currently reflects mozilla/rhino HEAD + enhancements for JSDoc)
- Removed jsdoc/util/global; new Rhino fork provides a `global` alias
  just like Node.js
- Moved most of jsdoc.js into cli.js, and refactored for clarity