Move variable marker size functionality into base ScatterPlot class
A first pass at allowing variable sized markers in a colormapped scatter plot
An example scatter plot with variable size and color symbols
Re-enable use of draw_path_at_points() method
Use bruteforce render method with variable size symbols in ColormappedScatterPlot
Update title for the view for colormapped variable sized scatter plot example
Eliminate rendundant marker rendering functions
Pass point mask to marker rendering function
Fix marker_size indexing for ColormappedScatterPlot
Use itertools to avoid unnecessary array and list creation
Fix example docstring, add to demo application.
Correct typo, comment about deprecating class.
Minor cleanups to ScatterPlot.
Simplify variable size scatterplot example.

Since it is not that special anymore, I simplified it and moved it to the
'basic' directory. It was also added to the demo application.
DOC Updated docs.
Merge pull request #101 from enthought/feature-scatterplot-merge

Allow variable symbol sizes in ScatterPlot