* Extension that does something like this:
use Rack::Cache, :backend => :memcached
* `sinatra-smart-cache`: update cache header only if arguments are more
restrictive than curent value, set caching headers that way for most helper
methods (i.e. `sass` or `send_file`)
* Some verbose logging extension: Log what filters, routes, error handlers,
templates, and so on is used.
* Form helpers, with forms as first class objects that accepts hashes or
something, so the form meta data can also be used to expose a JSON API or
similar, possibly defining routes (like "Sinatra's Hat"), strictly using
the ActiveModel API.
* Extend `sinatra-content-for` to support Liquid, Radius, Markaby, Nokogiri and
Builder. At least the first two probably involve patching Tilt.
* Rewrite of `sinatra-compass`?
* Helpers for HTML escaping and such.