WIP: refactor into stream interface

Hey!

This is an attempt to the refactoring design discussed in MAAS week.

@robert-chiniquy worked on the original version and then we worked on this together.

Currently it's on `443` so either use `sudo` or change the port number in the code :-)

```
npm install # install dependencies
make # generate certificate
sudo node examples/heartbeats-only.js
```

Any thoughts?
We also may or may not want to be able to delegate TLS longterm and have the connection connect in the clear. Out of scope for this PR though.