Make it clear whcih member s are internal and external

include/ucore/ucore_timers.h

@@ -22,7 +22,7 @@ enum {
 
 typedef void (*uc_timer_cb)(struct UCTimers *timers, struct UCTimer *timer);
 struct UCTimer {
-    //internal members 
+    //Internal members 
     RBNode rb_node; //the RBNode will hold a data pointer to the
                     //the UCTimer it's a member of. We might get rid of that member, and use CONTAINER_OF
                     //to find the UCTimer from a RBNode
@@ -34,6 +34,8 @@ struct UCTimer {
     unsigned char state;
     TAILQ_ENTRY(UCTimer) ready_entry; //entry in ready_list in UCTimers
 
+    //External members
+
     //callback function
     uc_timer_cb callback;