Auto-build binaries on release

[tptee]

Binaries now build for linux/osx/win on the most recent tag (or when [publish binary] is in the commit message).

TODO:

• Revert all references to tptee back to audreyt
• Use a contributor's Appveyor account and enable builds for this repo
• Use a contributor's encrypted Github personal access tokens for publishing binaries (https://github.com/bchr02/node-pre-gyp-github#configuration)

If you're comfortable with it, you could add me as a contributor to finish up the remaining tasks. No worries if not!

You can check out a working release at https://github.com/tptee/node-webworker-threads/releases