Optimise interpreter to process whole productions at a time based on datastring, instead of bit-by-bit.

[hornc]

Instead of processing the program string symbol-by-symbol (current method), we can speed things up by dividing the program string into different length productions (by splitting on ;) and examining the datastring for runs of 0s followed by a 1 to find the next production to append to the right of the datastring and delete n bits from the left.

This means than we won't be doing processing for every command in an inactive production.