Extract methods to decode and encode URI segments

I wonder if we might want to roll our own eventually, seeing the state
of Ruby URI encoding/decoding methods are kinda of a mess.

- URI.encode_uri_component encodes ~ as %7E, which is not what we
  want.
- ERB::Util.url_encode does not encode ~, but has no symmetric
  ERB::Util.url_decode method.

lib/route_downcaser/downcase_route_middleware.rb

@@ -62,7 +62,7 @@ def downcased_path(uri)
     end
 
     def downcase_path_segment(segment)
-      URI.encode_www_form_component(URI.decode_www_form_component(segment).downcase)
+      uri_encode(uri_decode(segment).downcase)
     end
 
     def path(uri)
@@ -77,6 +77,14 @@ def has_querystring?(uri)
       uri_items(uri).length > 1
     end
 
+    def uri_decode(uri_segment)
+      URI.decode_www_form_component(uri_segment)
+    end
+
+    def uri_encode(uri_segment)
+      URI.encode_www_form_component(uri_segment)
+    end
+
     def uri_items(uri)
       uri.split("?", 2)
     end