new: add pool server handler

examples/server/main.c

@@ -21,7 +21,7 @@ int main(int argc, char *argv[]) {
     goto end;
   }
 
-  if (!lm_ctx_pools_serve(&ctx, argv[1])) {
+  if (!lm_ctx_pools_serve(&ctx, argv[1], 10)) {
     printf("failed to serve the pools: %s (%d)\n", lm_strerror(), lm_error());
     goto end;
   }