moved the internals queue() and css() to NProgress.Internals so that the rest of the app, which uses NProgress, can also use these.
whitespace police
mention the LESS to CSS conversion in the docs.
- make queue chainable and fix minor bug when queue.next() would be invoked manually from inside another dequeued function.

- updated / augmented the documentation with the current public and 'internal' API.
fixups - fix crashes