add Command::Unit to describe similar fields between main command and motions

src/core/Command.h

@@ -33,18 +33,24 @@ public:
             BACK_UP_TO_CHAR,
             BACK_ON_TO_CHAR,
         };
+    };
 
+    struct Unit
+    {
         uint32_t id;
         uint32_t count;
         uint32_t following_char;
+
+        Unit()
+        {
+            id = 0u;
+            count = 0u;
+            following_char = 0u;
+        }
     };
 
-    uint32_t id;
-    uint32_t count;
-    uint32_t following_char;
-    Motion motion;
-
-    Command();
+    Unit main;
+    Unit motion;
 };
 
 #endif