GET route /public AKA Static file server

[glrta]

Serve up the files from the public folder!

• [x] route starts with /public/ added to router.js
• [x] handler function in handlers.js
• [x] parses req.url into filename and extension
• [x] if file exists return it with correct mime type
• [ ] if not then 302 redirect to /public/404.html