Issue #103 - Ordinal axis grids not being drawn, plus: * Ordinal gridlines. * Control whether or not the last line of the grid is shown through xAxisEndLine and yAxisEndLine chart options, and their styling through same named extension points. * The main axis rule, its ticks and labels, are now drawn on top of the chart bars. * Added some Z-order support to protovis to support described ordering (see pvc.js). * The value of 0-value bars is not drawn (because there really is no bar drawn) * In non-stacked bar charts, bar groups (corresponding to 1 category and multiple series) are now drawn aligned at the center and not at one of the sides of each category panel. This allows for an even space to the grid lines on each side. * Existence of null values on the data set caused errors in calculating scales' maximums. * Missing min-range value, on some cases, on a linear axis.
Issue #103 - Ordinal axis grids not being drawn, plus:
* Ordinal gridlines.
* Control whether or not the last line of the grid is shown through xAxisEndLine and yAxisEndLine chart options, and their styling through same named extension points.
* The main axis rule, its ticks and labels, are now drawn on top of the chart bars.
* Added some Z-order support to protovis to support described ordering (see pvc.js).
* The value of 0-value bars is not drawn (because there really is no bar drawn)
* In non-stacked bar charts, bar groups (corresponding to 1 category and multiple series) are now drawn aligned at the center and not at one of the sides of each category panel. This allows for an even space to the grid lines on each side.
* Existence of null values on the data set caused errors in calculating scales' maximums.
* Missing min-range value, on some cases, on a linear axis.

diogofscmariano/cdf,dcleao/cdf,dcleao/cdf,afrjorge/cdf,gcnonato/cdf,carlosrusso/cdf,afrjorge/cdf,Aliaksandr-Kastenka/cdf,miguelleite/cdf,e-cuellar/cdf,akhayrutdinov/cdf,webdetails/cdf,carlosrusso/cdf,jvelasques/cdf,e-cuellar/cdf,davidmsantos90/cdf,webdetails/cdf,krivera-pentaho/cdf,eliofreitas/cdf,pamval/cdf,scottyaslan/cdf,scottyaslan/cdf,eliofreitas/cdf,scottyaslan/cdf,Tiger66639/cdf,davidmsantos90/cdf,dcleao/cdf,carlosrusso/cdf,e-cuellar/cdf,bytekast/cdf,Aliaksandr-Kastenka/cdf,Tiger66639/cdf,gcnonato/cdf,krivera-pentaho/cdf,jvelasques/cdf,akhayrutdinov/cdf,bytekast/cdf,pamval/cdf,diogofscmariano/cdf,eliofreitas/cdf,pedrofvteixeira/cdf,miguelleite/cdf,pamval/cdf,diogofscmariano/cdf,Tiger66639/cdf,jvelasques/cdf,pedrofvteixeira/cdf,afrjorge/cdf,bytekast/cdf,webdetails/cdf,akhayrutdinov/cdf,gcnonato/cdf,davidmsantos90/cdf,plagoa/cdf,plagoa/cdf,krivera-pentaho/cdf,plagoa/cdf,miguelleite/cdf,Aliaksandr-Kastenka/cdf,pedrofvteixeira/cdf