Bump Middleman to 3.0.13

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Create separate rackup configuration for production

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Use stock Rack::TryStatic from rack-contrib

Signed-off-by: Alex Coles <alex@alexbcoles.com>