plugins_exts FEATURE added printer_tree callbacks

A new interface has been added that allows the plugin to add nodes
to print a YANG tree diagram and also change the appearance of nodes.
diff --git a/src/plugins_exts/nacm.c b/src/plugins_exts/nacm.c
index 2ba5692..5ab8daa 100644
--- a/src/plugins_exts/nacm.c
+++ b/src/plugins_exts/nacm.c
@@ -163,6 +163,8 @@
         .plugin.parse = nacm_parse,
         .plugin.compile = nacm_compile,
         .plugin.printer_info = NULL,
+        .plugin.printer_ctree = NULL,
+        .plugin.printer_ptree = NULL,
         .plugin.node = NULL,
         .plugin.snode = NULL,
         .plugin.validate = NULL,
@@ -177,6 +179,8 @@
         .plugin.parse = nacm_parse,
         .plugin.compile = nacm_compile,
         .plugin.printer_info = NULL,
+        .plugin.printer_ctree = NULL,
+        .plugin.printer_ptree = NULL,
         .plugin.node = NULL,
         .plugin.snode = NULL,
         .plugin.validate = NULL,
@@ -191,6 +195,8 @@
         .plugin.parse = nacm_parse,
         .plugin.compile = nacm_compile,
         .plugin.printer_info = NULL,
+        .plugin.printer_ctree = NULL,
+        .plugin.printer_ptree = NULL,
         .plugin.node = NULL,
         .plugin.snode = NULL,
         .plugin.validate = NULL,
@@ -205,6 +211,8 @@
         .plugin.parse = nacm_parse,
         .plugin.compile = nacm_compile,
         .plugin.printer_info = NULL,
+        .plugin.printer_ctree = NULL,
+        .plugin.printer_ptree = NULL,
         .plugin.node = NULL,
         .plugin.snode = NULL,
         .plugin.validate = NULL,