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 add a footnote to clarify index keys may also be used.  If you don't like footnotes, then I think key indices should be mentioned here (use simple sentences rather than adding it to the current compound sentence).

This is part of the official PyToolz documentation, and I think we should at least mention best practices.