Remove typed_* data structures and related files
Move internal headers into src/
Remove use of alloc_cb callback

It is useless since we can replace
  set(n, data, (gds_alloc_cb)data_alloc);
by
  set(n, data_alloc(data));

or
  get(n, (gds_alloc_cb)data_alloc);
by
  data_alloc(get(n));