Changes an extended attribute. \n
* The data will be internally duplicated. \n
* If data is NULL and count==0 the attribute is removed. \n
* If count is -1 and data_type is IM_BYTE then data is zero terminated.
* See also \ref imDataType.
*
* \verbatim image:SetAttribute(attrib: string, data_type: number, data: table of numbers or string) [in Lua 5] \endverbatim
* If data_type is IM_BYTE, a string can be used as data.
* \ingroup imgclass
Changes an extended attribute. \n * The data will be internally duplicated. \n * If data is NULL and count==0 the attribute is removed. \n * If count is -1 and data_type is IM_BYTE then data is zero terminated. * See also \ref imDataType. * * \verbatim image:SetAttribute(attrib: string, data_type: number, data: table of numbers or string) [in Lua 5] \endverbatim * If data_type is IM_BYTE, a string can be used as data. * \ingroup imgclass