Add `debugger` support
Would be nice to do something like https://github.com/AnimaApp/CocoaPowder when writing `debugger`. Should be possible with a small babel plugin: https://github.com/babel/minify/blob/master/packages/babel-plugin-transform-remove-debugger/src/index.js

Unfortunately, it doesn't work right now because of http://sketchplugins.com/d/265-disablecocoascriptpreprocessor-and-error-stack