rope: make rope library macro template

Rope library stores alloc, split and free functions by pointer,
that is a huge slog at performance, as any other virtual
function call. There is no reason, why the rope library may not
become a template, except historical ones.

The patch not only removes virtual functions, but also makes rope
deletion almost no-op in case if free() function is not defined.

A second motivation point of that patch is that original rope
structure was too big. Again, because it stored several pointers
to functions. In forthcoming patches on #1261 multiple ropes can
be created per each update, so it makes sense to reduce size of
this structure.