add API for getting "startValue" and "endValue" from dataZoomModel
add API for getting "startValue" and "endValue" from dataZoomModel

ecomfe/echarts,xiayz/echarts,100star/echarts,starlkj/echarts,chenfwind/echarts,starlkj/echarts,hexj/echarts,ecomfe/echarts,hexj/echarts,xiayz/echarts,hexj/echarts,apache/incubator-echarts,100star/echarts,chenfwind/echarts,apache/incubator-echarts,starlkj/echarts