Add option to ignore certain files

[leoasis]

In my current app I have some files that have global css, which are just required, and they are even only required in the server (guarded by an if). It'd be useful to be able to avoid attempting to transform those cases, probably by supporting the ignore option in the same way the require hook allows.

What do you think?

[michalkvasnicak]

Hello I am sorry for a delay but I don't have time currently. I will look at it but don't know when. But feel free to create a PR if you can :)