- Support for dynamic downsampling and view clipping in PlotDataItem / PlotItem
  - fixed __truediv__ handling
  - ViewBox updates to fix aspect locking (still broken)
  - AxisItem tries to be more clever about when to display tick text
  - Fix segmentation fault caused by exception inside GraphicsItem.paint()
  - Added 'x' scatter plot symbol
  - pg.mkPen supports dashes