Optimise the optimisation stage by creating a new structure to represent instructions in bytecode.

[drwhut]

As of now, the optimisation stage will change every other instruction if needed every time bytecode is removed!

Instead, maybe "mark" bytecode to be removed over time, then remove the bytecode all at once at the end, changing instructions if necessary?

[drwhut]

I am going to change the nature of the issue, and move it to the 0.4.0 update, for a simple reason.

In order to make the optimisation process as simple as possible, it would require representing each instruction in a nicely-formatted structure. But using that new structure would be very handy elsewhere in the code as well, e.g. code generation.

The reason I am changing the milestone is this change would not affect GUI editors in any way.