move stuff around, fix strset issue

build.bx

 includes := include/lang2
-files := src
+files := lib cmd

include/lang2/vm/vm.h

 	l2_word data[];
 };
 
-void l2_vm_array_mark(struct l2_vm_value *arr);
-
 struct l2_vm_namespace {
 	struct l2_vm_value *parent;
 	size_t len;
 	l2_word data[];
 };
 
-void l2_vm_namespace_mark(struct l2_vm_value *ns);
 void l2_vm_namespace_set(struct l2_vm_value *ns, l2_word key, l2_word val);
 l2_word l2_vm_namespace_get(struct l2_vm_value *ns, l2_word key);
 

src/strset.c → lib/strset.c

 		for (size_t j = 0; ; ++j) {
 			size_t index = (h + j) & set->mask;
 			char *k = set->keys[index];
-			if (k == NULL || strcmp(oldkey, k) != 0) {
+			if (k != NULL) {
 				continue;
 			}
 
 		if (k == NULL) {
 			set->keys[index] = *str;
 			set->vals[index] = set->next++;
+			set->len += 1;
 			*str = NULL;
 			return set->vals[index];
 		} else if (strcmp(*str, k) == 0) {
 		if (k == NULL) {
 			set->keys[index] = strdup(str);
 			set->vals[index] = set->next++;
+			set->len += 1;
 			return set->vals[index];
 		} else if (strcmp(str, k) == 0) {
 			return set->vals[index];