Add API routes

[lucacasonato]

The user should be able to add routes to pages/api that should be treated as server side API endpoints rather than HTML pages. The signature for an API route would look something like this:

// pages/api/redirect.ts

export default async (req: Request): Promise<Response> => {
  return Response.redirect(req.headers.get("X-Redirect-To"), 307); 
}