[ANALYZER-1545] - Ability to show data labels on charts and visualizations.
* Added a new plot pvc.visual.Plot option, "ValuesOverflow", with values "show", "trim", and "hide" (the later is the default).
** The option is currently supported by the chart types: Bar, NormalizedBar, Waterfall, Pie, Treemap and Sunburst.
* Fixed regression of pvc.BarAbstractPanel#pvBarPanel field; was pointing to the CCC Sign object, instead of to the corresponding pv.Mark.
* Fixed regression of bar-family charts' and of the pie chart values label, that would become hidden for certain unrelated configurations.
* Removed the pvc.visual.SunburstPlot's "SubValuesVisible" option, created to satisfy an Analyzer use case, but that can equally and better be handled on the ccc_wrapper.
* Improved the valuesOptimizeLegibility option, by only applying it when the label is considered inside the associated visual element.
* Update to latest protovis, containing related changes.
[ANALYZER-1545] - Ability to show data labels on charts and visualizations (Docs and Examples)
* Documented the new ValuesOverflow plot option.
* Updated the documentation of the ValuesOptimizeLegibility plot option to be on pair with latest improvements.
* Improved the description of the related ValuesAnchor plot option.
* Added documentation for the related and missing textMargin option of the Label extension point.
* Changed a few of the site's examples to show off the new feature.
Merge pull request #53 from dcleao/values-overflow

[ANALYZER-1545] - Ability to show data labels on charts and visualizations