Add configurability to default scrubs

[etceterum]

We've found a need to disable some of the default scrubs in our project so we forked your repo and implemented it - and now would like to give back.

[etceterum]

@ankane Thank you for the feedback and sorry for being slow with my response. I will address your comments in the next few days

[etceterum]

I believe I have all of your findings addressed now @ankane, please let me know if any other changes are needed.

[ankane]

Looks great, thanks @etceterum!

[etceterum]

Thanks very much @ankane! I don't see the new version at rubygems (eager to switch us back from fork to the official branch 😄 - and I am now wondering if that's because I forgot to bump the version inside version.rb 🤔

[ankane]

Just pushed a new release.