more eo simplified to use Eina_Slice instead of pointer to.

more eo simplified to use Eina_Slice instead of pointer to.

Working directly with Eina_Slice is easier than a pointer to it,
requires no validation of the pointers and is cheap since it's just
putting together size_t + void*.

However we can't hint the user of 'const(Eina.Slice)' properties as
Eolian is incorrectly generating getters as:

   const Eina_Slice class_property_get(...)

which is makes compilers complain about ignored qualifiers:

   ../src/lib/ecore/efl_io_copier.eo.h:329:7: warning: 'const' type qualifier on return type has no effect [-Wignored-qualifiers]

Leave some TODO so @q66 can fix those.