prerendering routes

[terrablue]

Use cases: static websites, partially static websites.

Possible approaches:

• some (or all) routes are SSR'd at startup into static files, using some pseudo-request object, because they only contain static information
• blockers: using request.session in a route should throw a CannotPrerenderError, because sessions are unique to users; same for using request.store
• we could prerender an entire application, add a export const prerender = true; to a route file (would apply only to the GET route, in such a case the route file may not contain other HTTP verbs), and/or automatically prerender all routes which look like filenames: for example, routes/sitemap.xml.js