void render(Orgitem item,
Renders the data to the specified Orgitem.
Note: When this method is called, the orgitem should have no child at all.
Orgnode is only component that allowed to be item's children.
Do not append any Orgchildren to item in this method, an Orgchildren will be appended afterward.
item - the Orgitem to render the result.
data - that is used to render the Orgitem
index - the index of the data that is currently being rendered.
Notice the index is the order of the siblings (i.e., data that belongs to the same parent).