The ":" now takes care of scanning for ";". Conceptually, having
";" as an immediate word is slightly simpler than the approach in
this commit, but when bootstrapping is involved, this simpler
approach gets murkier.
Moreover, it got even murkier-er when trying to de-stabilize EXIT,
so here we are.
Instead of having wordref point to core word routines, I made them
into word 4 word types. It liberates space into the stable ABI and
should make porting to other arches easier.
I'm also thinking of combining word type with the namelen field
for precious bytes saving, but not now...
This allows us to move words like ABORT" to xcomp-core, which is
I think the last roadblock before being able to unify all drivers
into a single xcomp layer.
