better deprecation message UX

[jonathanong]

when a method is deprecated, it would be nice to show where it is being called so that devs know where to change it as well as which module author to blame. this would allow making breaking changes to be much easier in the future. this idea has helped express users upgrade through breaking changes seamlessly.

See: https://github.com/dougwilson/nodejs-depd

[bnoordhuis]

It already works like that, only it wasn't documented until now (but see #191.)

[bnoordhuis]

Closing because of commit 8b04161. If you want to implement your suggestion from #191, cc me on the PR and I'll review it. Cheers.