Move working chat into `example/`

Putting these away in here so we can set up a bit of framework for people to
build in, leaving the example accessible for reference.
Copy framework bits into the root dir

Here's the starting point for class. We'll walk through pieces in roughly this
order:

- Create your textarea for the chatroom
- Create your input line and send button
- Initialize PubNub and subscribe to the chat channel
- Print received messages into the chat textarea
- Wire up the send button to send your message
Add standard requirements to get started
Describe how computers find and talk each other

We'll go over this in person, but if the kids (or their grownups) want to read
on their own or look at it again later, here it is.