provide ##core#inline-routines for cheap SRFI-4 vector primitives

[felix winkelmann]

XXXvector-length, XXXvector-ref and XXXvector-set! would be much more efficient if routines callable via ##core#inline[_allocate] would be available for them (just as it currently is for, say, vector-ref). Since the structure-tag is not available in the C runtime, it has to be explicitly passed, e.g.

C_word C_i_XXXvector_ref(C_word tag, C_word vec, C_word index);
C_word C_i_XXXvector_set(C_word tag, C_word vec, C_word index, C_word x);
C_word C_i_XXXvector_length(C_word tag, C_word vec);

(need allocating ..._ref for f64/s32/u32 vector)

Note that the existing C_a_i_f64/S32/u32vector_ref are incorrectly named and should be C_u_a_i_... or something similar.

[felix winkelmann]

Note: renaming C_a_i_XXXvector_ref and friends will require updating the names in unboxing.scm.

[sjamaan]

Putting it on the roadmap, tentatively for 5.1

[sjamaan]

We could also simply make the tags available in a global variable, like we do (or did) for the extended numeric types and the error-hook. This would be slightly more flexible, for example if we changed the representation to have a dedicated custom type.

[sjamaan]

Getting ready for 5.1, moving tickets which won't make it in to 5.2.

[sjamaan]

Implemented with ea10de3