yanglint FEATURE printing modules for YANG Tree

For YANG Tree Diagrams printing it's more readable to print a blank
line between modules. Based on mbj4668/pyang#681
diff --git a/tools/lint/cmd_print.c b/tools/lint/cmd_print.c
index 7d68823..823ca7b 100644
--- a/tools/lint/cmd_print.c
+++ b/tools/lint/cmd_print.c
@@ -93,8 +93,9 @@
     LY_ERR erc;
     char *name, *revision;
     ly_bool search_submodul;
+    const int stop = argc - optind;
 
-    for (int i = 0; i < argc - optind; i++) {
+    for (int i = 0; i < stop; i++) {
         name = argv[optind + i];
         /* get revision */
         revision = strchr(name, '@');
@@ -113,6 +114,10 @@
         }
 
         if (erc == LY_SUCCESS) {
+            /* for YANG Tree Diagrams printing it's more readable to print a blank line between modules. */
+            if ((format == LYS_OUT_TREE) && (i + 1 < stop)) {
+                ly_print(out, "\n");
+            }
             continue;
         } else if (erc == LY_ENOTFOUND) {
             if (revision) {