Improve middleware with a better static file filter.

Hi, 

I just added a better static file filter for middleware, it basically filter out static files ending with `html|png|css|jpg|jpeg|gif|js|ico|xml|rss|txt`, with or without revision query params (example: `script.js?v=h4s1-l `). This is inspired by a typical nginx server config file, and modified to support revision params. Stumbled upon this because the original dynamic request filter config didn't work with my backend. 

Although this file should be changed frequently based on user's backend but I think this is general enough to support most server config.

Cheers!
Marani.