Switch between different .npmrc files

 If you use a private npm registry, you know the pain of switching between a
 bunch of different .npmrc files and manually managing symlinks. Let that be a
 problem no more! npmrc is here to save the day, by making it dead simple to
 switch out your .npmrc with a specific named version. It also tries to protect
 you from your own stupid self by making sure you don't accidentally overwrite
 an .npmrc that you actually want to keep.