Fixed rotateLabels option for multiBarCharts

Replaced 'text-transform' with correct attribute 'text-anchor' to set
rotation center of labels.
Adjust axis labels on update rather than enter.

This allows an axis to change orientation and have the tick label respond accordingly.
Issue #73 Error: Invalid value for <rect> attribute y="NaN", height="NaN"
Use the formatter that belongs to yAxis of the series to format the y value of a tooltip, instead of basing it on the series chart type.
Multi bar chart legend width computed with 'showControls' respect
#69: adding a way to color individual bars (rather than the whole series as it is done right now).  Leaving the previous behavior as the default.
Horizontal barcan nopw stack with both positive and negative, verticaly aligned values with center of bar
Positive and negative stacked horizontal withunique colors per group
Fixed issue with custom group color and disabling series on the horiontal bar chart
Added barColor fucntionality to multibar to imitate what I did for multibarHorizontal
Fixed max and min calculations for multibar stacked
Made tooltip look a little sexier
Made tooltip look a little sexier
Made tooltip look a little sexier
add property for label radius
fixed js error in scatter voronoi mouseover
Merge branch 'master' of https://github.com/novus/nvd3
keep the size of pie chart when change the svg size
Add support for startAngle and endAngle on pie chart
add key description to display in tooltip