Add examples for 404 and static file handlers

[JeremyChaseGawker]

Examples for custom 404 pages and serving static assets would be helpful.

[futurechimp]

I've done up the static files section, still need to add in the custom 404 pages stuff.

[futurechimp]

@JeremyChaseGawker does this meet your needs as far as custom 404 pages goes?

http://www.scalatra.org/stable/book/#Rendering_a_404_page_using_the__code_notFound__code__handler