Add streaming analytics doc page

This will probably become a blogpost (though not until the work is actually in to the various `*toolz` projects.)

@eigenhombre The join PR benefited significantly from your comments.  Your perspective would be appreciated here.
I think what you have is pretty clear, so I say keep it.  If it starts a Python 3 conversation, then so be it!

I think the reason pattern matching in signatures was dropped is that it complicated APIs, very few people used it anyway (or so they claim), and the same functionality can be accomplished with only one additional line:
```python
def binop(total, item):
    id, name, bal, gend = item
    return total + bal
```