Related:

#290
#261

The new flexible states are here! With these new states it is rather easy to install new variables, which can have fixed lengths (real, vec, vec6...) or variable lengths depending on the instance (e.g. lines as vec3 and rods as a combination of vec7 and vec6).

It is fairly optimized, avoiding some copies here and there. However, the implementation comes to a performance cost, becoming as twice slower as the previous implementation. I suppose some other optimizations can be made to avoid some copies. I just do not know if it is worth the effort, as long as we are bringing --hopefully soon-- a time scheme which will make simulations waaaaaay faster.