module Roda::RodaPlugins::Caching::ResponseMethods

def cache_control(opts)

http://tools.ietf.org/html/rfc2616#section-14.9.1
See RFC 2616 / 14.9 for more on standard cache control directives:

# => Cache-Control: public, max-age=60
response.cache_control public: true, max_age: 60

Options can also contain value directives (:max_age, :s_maxage).
:no_store, :must_revalidate, :proxy_revalidate), with true as the value.
Options can can any non-value directives (:public, :private, :no_cache,
Specify response freshness policy for using the Cache-Control header. 
def cache_control(opts)
  values = []
  opts.each do |k, v|
    next unless v
    k = k.to_s.tr('_', '-')
    values << (v == true ? k : "#{k}=#{v}")
  end
  @headers[RodaResponseHeaders::CACHE_CONTROL] = values.join(', ') unless values.empty?
end