Added a chapter on creating and using app.js.
Added a section on how to configure routing with app.js.
Copy edited the middleware section.
Added note about Mojito v0.9 and middleware changes.
Deprecated routes.json doc, replaced exs w/ app.js for routing, creating routing chapter.
Adding routing documentation.
Merge pull request #1362 from zhouyaoji/docs_app.js_chapter

[docs] Added chapter covering app.js, section on routing config w/ app.js in config chapter, and edited middleware section.