Consider having `routes.json` at the top-level

After #225 the content of the file had to be moved to `lib` (where all the JS lives for Franklin). However, it's not contirbutor-friendly for the file to remain there instead of being at the top-level.

Question posed is as follows: could we have `routes.json` at the top-level while being compatible with all browsers?

- If yes, a PR should add this
- If no, close this issue

