uint8Numbers: a table containing uint8 numbers. Invalid byte number will be packed in an undefined manner.
startUint8Index: the zero-based index from which on data should be packed. Can be omitted in which case 0 is used
uint8count: the amount of uint8s that should be packed. Can be omitted in which case 0 is used (which indicates that the maximum available uint8s should be packed from the indicated startUint8Index)