new: general update pattern example

Started new general update pattern example based on
Mike's join tutorial

http://bl.ocks.org/mbostock/3808218

Also updated venn to latest strokes (with better maps).
general update pattern: finished 2 and 3.

Straightforward port. Nice to see transitions working.
updated general-update and venn to strokes-0.4.0

Both were using recent functionality. Now on
an official version.