Upgrades the node environment to NodeJS 7.6.0. Functions can now use async/await and promises; they can return a promise instead of using a callback. The change preserves compatibility with the callback style.
* Upgrade node environment to Node.js 7.6.0+
* Bump package version
* Preserve compatibility for callbacks
* Cleanup
* Re-add hello callback example
* Make sure not returning won't blow everything up
* Update stock example with request promise
