Unfortunately, due to how vectors are implemented, pointers to them
are unstable. We need to box them one more time (therefore adding a
level of indirection) in order to stabilise them. This is annoying
but currently necessary.
Even if we implemented vectors as {u64, u64, ptr} instead of {u64,
u64, bytes...}, we'd still have the same problem at access - two
levels of indirection. I guess size and capacity checks would be one
level of indirection which is nice at least, but we're already screwed
at the point of doing lookup either way.
