Introduce reference type, use vectors of SCM.
* mes.c (type): Add REF.
(scm_t): Add ref, change vector to *scm_t. Update users.
(alloc): New function.
(cons, make_char, make_macro, make_number, make_string,
internal_make_symbol, make_vector): Use it.
(make_ref): New function.
(vector_entry): New function.
(make_vector, list_to_vector, vector_set_x): Use it.
(vector_ref): Dereference REF entry.
(display_helper): Handle REF.
* lib.c (vector_to_list): Handle REF.
* type.c (ref_p): New function.
* tests/vector.test (vector list): New test.
Bugfix vector-ref.
* mes.c (vector-ref): Make copies of simple values. Fixes lalr.
* tests/vector.test (vector-set! 3): New test.