strset, strmap: invert iterator function meaning. Make a false return abort the iteration, not true. The old way makes sense for search functions (true == I found it), but other kinds of iteration are more common (brute force search is probably dumb).
setset: fix API to match strmap and common sense. strset_set -> strset_add strset_clear -> strset_del strset_test -> strset_get strset_destroy -> strset_clear
strset: allow const arguments to strset_iterate().
strset: set errno to ENOENT even if we return NULL. It seems redundant: strset_test() and strset_clear() can only return NULL when the string is not a member. However, it became clear in writing ccan/tsort that it's much more convenient for callers if we set errno in this case too, so they can pass it up.
strset: set errno on strset_add failures.
strset: new module using critbit trees. Not as fast as using htable, but simple and provides order and prefix ops.