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
Reorganized setup.py code
Added "deb" setup command
more reorganization to make setup-helpers code more generic
Updated build system to use pybuild
- now generates python-pyqtgraph, python3-pyqtgraph, and python-pyqtgraph-doc packages
- `python setup.py sdist deb` works
Nicer range for value histogram of integer images.

When an ImageItem's data has an integer dtype, this patch ensures that
each bin of the LUT histogram contains the same number of integer
values, in order to avoid "spikes" in the histogram that are merely due
to some bins covering more integer values than others.

This commit needs testing (it was rebased from an old commit).
Merge remote-tracking branch 'anntzer/integer-image-histogram-range' into integer-image-histogram-range
ImageItem.getHistogram is more clever about constructing histograms:
  - integer dtype images now have integer-aligned bins, with bin number
    determined by a target value
  - step size is automatically chosen based on a target image size
  - bins and step arguments have default values 'auto'
Merge branch 'integer-image-histogram-range' into develop

ImageItem.getHistogram is more clever about constructing histograms:
  - integer dtype images now have integer-aligned bins, with bin number
    determined by a target value
  - step size is automatically chosen based on a target image size
  - bins and step arguments have default values 'auto'
fixed division by zero
Merge remote-tracking branch 'gpoulin/scatter_optim' into scatter-optim

Conflicts:
	pyqtgraph/functions.py
	pyqtgraph/graphicsItems/AxisItem.py
cleanups
LegendItem bugfix
drawSymbol is module-level funct, not class method