patch 8.1.2243: typos in comments

Problem:    Typos in comments.
Solution:   Fix the typos. (Dominique Pelle, closes #5160)  Also adjust
            formatting a bit.
diff --git a/src/macros.h b/src/macros.h
index f670046..5da0e5c 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -335,7 +335,7 @@
 	} \
     } while (0)
 
-/* Wether a command index indicates a user command. */
+/* Whether a command index indicates a user command. */
 #define IS_USER_CMDIDX(idx) ((int)(idx) < 0)
 
 // Give an error in curwin is a popup window and evaluate to TRUE.