feat(middleware): add middleware stack builder

lib/prism/middleware.rb

@@ -0,0 +1,25 @@
+module Prism
+  class MiddlewareStack
+    def initialize
+      @entries = []
+    end
+
+    def use(middleware, *args, **kwargs, &block)
+      @entries << [middleware, args, kwargs, block]
+    end
+
+    def build(app)
+      @entries.reverse.reduce(app) do |inner, (middleware, args, kwargs, block)|
+        if kwargs.empty?
+          middleware.new(inner, *args, &block)
+        else
+          middleware.new(inner, *args, **kwargs, &block)
+        end
+      end
+    end
+
+    def empty?
+      @entries.empty?
+    end
+  end
+end