Allow passing through unrecognized options to underlying module.

[Jeremy-Walton]

For instance, if I create a Browserify asset, I should be able to pass in any Browserify option to the asset. If it is unrecognized by the asset, it should be passed to Browserify directly.

In my situation, I want to use the Browserify 'path' option which lets you specify the root of your project. That way, when you use require(), you can use the absolute path instead of relative paths. Using rack assets doesn't allow me to use this option.