[+] Add edge postEffect

[+] Support export to image through saveAsImage and getDataURL

[+] Add mouse event.

[^] Improve SSAO postEffect

[^] Fix label in axisPoint not disappear bug. See https://github.com/ecomfe/echarts-gl/issues/42

[^] Fix bar3D data item opacity can't be set bug. See https://github.com/ecomfe/echarts-gl/issues/47

[^] Fix bar3D emphasis wrong when some item are set transparent.

[^] scatterGL support tooltip. See https://github.com/ecomfe/echarts-gl/issues/35