optimize ScatterPlotItem with pxMode=True
Correct comment in examples/ScatterPlot.py
Modify for loop into map in ScatterPlotItem.py
Improve ScatterPlotItem
Slightly faster and more memory efficient, correct python 3 bug
Some few more optimization to ScatterPlotItem
Rename self.tar to self.target
Improve ScatterPlotItem.py
Add optimization for PySide, Plot only visible symbole, cache rectTarg
Clean ScatterPlotItem
Correct symbols position
Don't copy the context menu of ViewBoxes.

This allows customization of the context menu of a ViewBox simply by
calling viewbox.menu.addAction(...).  See issue #13.  Also some cleanup.
Override ViewBox.popup() to update menu before showing
Extend ViewBox menu in examples/contextMenu
ImageItem now has auto downsampling; seems to be working properly.
Still need auto clipping as well.
Use actions of ViewBox's contextMenu in full menu.

The main change is on `ViewBox.getContextMenus`, which now returns an
up-to-date of actions that `GraphicsScene.addParentContextMenus` can use.

Also, `getContextMenus` was given a default implementation in the base
class (falling back on `getMenu` if defined), and some cleanup was done.
fixed context menu handling for non-GraphicsItems
Merge branch 'dont-copy-context-menu' into develop
This allows ViewBox context menus to be modified by directly manipulating ViewBox.menu
corrected GradientWidget.__all__
Speedups for making ARGB arrays
Undo remove trailing whitespace
Merge branch 'master' into develop
Simplify to take transpose logic out of makeARGB function