- added ability for ScatterPlotItem to use arbitrary symbol shapes
- added scatter plot speed test for evaluating new methods
- added butterworth notch filter to flowchart library
- fixed bugs with ViewBox trying to close itself after python has started cleaning up
- fixed python 2.6 compatibility bug in PlotCurveItem
- fixed support for list-of-dicts and dict-of-lists input for PlotDataItem
- check to ensure Qt version is >= 4.7
- workaround for numpy segmentation fault
- several other minor updates and documentation changes
