Add files entry to package.json.
Add files entry to package.json.

Removes unnecessary files from the deployed package.

Deploying unnecessary files impacts the performance of `npm install` for everyone.

See: https://github.com/insin/package-config-checker

This PR was created using a series of both scripted and manual steps. I have done my best to make sure my modifications are correct, but I am creating similar PR for a lot of repositories today. So please, double check that I have included all the important files (and apologies if I've made some huge oversight).

request/tunnel-agent,mikeal/tunnel-agent