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.
This line has many parentheses, which may make it more difficult to comprehend.  Perhaps use `pluck(2)` instead of `map(get(2))`, or name the input function such as `sumbalance = compose(sum, map(get(2)))`.