Support custom cache control headers for static assets

[sivakumar-kailasam]

Allows users to configure cache control for the static assets. Addresses #41

[sivakumar-kailasam]

Another alternative could be passing an instance of https://github.com/expressjs/serve-static

[benkingcode]

Would love to get this in, I'd like my assets to be immutable rather than max-age=0. What is needed to get merged?

[mirague]

Same here, max-age=0 makes no sense for static assets.

Also, possible duplicate of #35

[sivakumar-kailasam]

Shucks, looks like #35 is much more flexible than this one, I can either improve or close this one in favor of it. Thoughts @arjansingh ?