objectHandle: handle of the object or script where you want to store your data, or sim_handle_scene if you wish to store the data with the scene.
dataName: a string that identifies the data. An empty string will remove all custom data blocks.
data: your custom data. If NULL, the current data under the specified dataName will be removed.
dataSize: the size of your custom data
The data will be copied to an internal buffer inside of the object or scene, and next time a scene or model is saved, will also be saved. The data buffer can be released after this call.