FLEX叠加柱状图（分层柱状图）

引用：http://zjkilly.iteye.com/blog/920956

一句话，设置type属性

"clustered": Values from different series are grouped by category. This is the default type.

"overlaid": Multiple values are rendered on top of one another by category, with the last series on top.

"stacked": Columns are stacked on top of each other and grouped by category. Each column represents the cumulative value of the columns beneath it.

"100%": Columns are stacked on top of each other, adding up to 100%. Each column represents the percent that it contributes to the sum of the values for that category