simu - rearrange some packages
simu - merge listprim2 and lower
simu - listprim2 more cleanup
simu - a slight modifcation on comments
tree->instruction-list moved into rules

I think the reason we need to turn data into instruction list
is because of the expansion of primitives,
and it's more reasonable to move this function there.
ex 5.21 - lower simu - code simplified