Can janus proxy a web page instead of an single target url

[chenliejun]

[Short description of problem here]

I am thinking:janus as an api gateway to proxy upstream api serice,can it proxy the total web page with sub request of css、js、png so on.

Reproduction Steps:

1. [First Step]
   Create an API Definition with
   Set the listen_path as :/something,
   Set the upstream target as: http://my.private.blogsite.com(some real blog site)
2. [Second Step]
   visit http://localhost:8080/something
3. [Other Steps...]
   got the page with single html,but the page's css、js、png got the 404 response（which are the request in the html some like:/css/blog.css、/js/jquery-1.11.3.min.js、/img/favicon.png）

Expected behavior:
proxy all the regular target ,just like nginx.as so the css、png、js can also be proxied

[Describe expected behavior here]
can the upstream target can be set with the same rule as listen_path,es：http://my.private.blogsite.com/*