Terminator iterator

Make Terminator an iterator over bytes. The implementation will be more sound because priority of symbols will be respected, and it will lower the allocation needed, making it (hopefully) faster.

According to the benchmarks which were added to the benches folder, after removing println!() statements which slowed the execution because of buffering, this implementation is 8x faster than the previous. No data were gathered concerning allocation but it should be lower by a fair margin, at least with slices (i.e. not the REPL)