Add More marker shapes ( square,triangle,diamond,cross,plus) for points


![chartmarker](https://cloud.githubusercontent.com/assets/8490104/4387579/c410d17e-43de-11e4-9316-8ffde4312d7d.jpg)
Make option to change pointDot Shape  ( square,triangle,diamond,cross,plus).
ex:
pointDotMarker:"square",