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 it could be made clear by showing the imports from toolz (as is typically done in other sections of the online documentation).  If we show all the imports near the beginning, then perhaps they can be grouped by primary functions being discussed:
```python
from toolz import groupby, valmap, reduceby, join
```
and additional functions:
```python
from toolz import compose, first, pipe, second, unique
from toolz.curried import get, map, pluck
```