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.
Great comments, Eric!! And I look forward to catching up w your blog post, Matt!

Sent from my iBrick

> On Jun 29, 2014, at 1:52 PM, Erik Welch <notifications@github.com> wrote:
> 
> In doc/source/streaming-analytics.rst:
> 
> > +succession, accumulating running totals for each key by combining each new
> > +value with the previous using the binary operator.  It can't accept full
> > +reduction operations like ``sum`` or ``min`` as these require access to the
> > +entire group at once.  Here is a simple example:
> > +
> > +.. code::
> > +
> > +   >>> def iseven(n):
> > +   ...     return n % 2 == 0
> > +
> > +   >>> def add(x, y):
> > +   ...     return x + y
> > +
> > +   >>> reduceby(iseven, add, [1, 2, 3, 4])
> > +   {True: 6, False: 4}
> > +
> Although simple, I expect this example will still require a non-negligible number of readers to think for themselves to figure out what is going on. reduce and reduceby can be difficult to grasp if one is not familiar with them and their API usage.
> 
> So, I would add a short sentence that explains what the above example does, such as:
> 
> The even numbers are added together (2 + 4 = 6) into group True, and the odd numbers are added together (1 + 3 = 4) into group False.
> 
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