tweaks: group the special keycodes for implanted strings together

This shows better that they are related.

src/definitions.h

@@ -214,16 +214,12 @@
 #define SHIFT_DELETE    0x45D
 #define SHIFT_TAB       0x45F
 
-/* A special keycode for when a string bind has been partially implanted. */
+/* Special keycodes for when a string bind has been partially implanted
+ * or has an unpaired opening brace, or when a function in a string bind
+ * needs execution or a specified function name is invalid. */
 #define MORE_PLANTS       0x4EA
-
-/* A special keycode for when a string bind has an unpaired opening brace. */
 #define MISSING_BRACE     0x4EB
-
-/* A special keycode for when a function in a string bind needs execution. */
 #define PLANTED_COMMAND   0x4EC
-
-/* A special keycode for when a function name in a string bind is invalid. */
 #define NO_SUCH_FUNCTION  0x4EF
 
 /* A special keycode for when <Tab> is pressed while the mark is on. */