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.
Perhaps link to the following, which discusses split-apply-combine in pandas:

http://pandas.pydata.org/pandas-docs/stable/groupby.html

Join is discusses the the section following this.