A Rack middleware that inserts a Moneta store in the environment and supports per-request caching via the the option `:cache => true`.

@example config.ru

  # Add Rack::MonetaStore somewhere in your rack stack
  use Rack::MonetaStore, :Memory, :cache => true

  run lambda { |env|
    env['rack.moneta_store'] # is a Moneta store with per-request caching
  }

@example config.ru

  # Pass it a block like the one passed to Moneta.build
  use Rack::MonetaStore do
    use :Transformer, :value => :zlib
    adapter :Cookie
  end

  run lambda { |env|
    env['rack.moneta_store'] # is a Moneta store without caching
  }

@api public