Thanks for this great plugin and keep up the good work!
I tested my page on http://gtmetrix.com/
And I got this varning about "?document-gallery-css=1&ver=2.0.3:1"
I dont know if someting needs to be changed or if this have someting to do with other plugins or wordpress itself but I wanted to report the issue.
Resources with a "?" in the URL are not cached by some proxy caching servers. Remove the query string and encode the parameters into the URL for the following resources:
Remove query strings from static resources
Most proxies, most notably Squid up through version 3.0, do not cache resources with a "?" in their URL even if a Cache-control: public header is present in the response. To enable proxy caching for these resources, remove query strings from references to static resources, and instead encode the parameters into the file names themselves.