Adds r command to replace a char

.gitignore

@@ -1,3 +1,4 @@
 hermes
 *.txt
 test*
+*.1.gz

hermes.c

@@ -1109,6 +1109,19 @@ void editorCommandKp(int c) {
     case '\033':
       if (E.mode == VisualMode) E.mode = CommandMode;
       break;
+    case 'r':
+      {
+        int c = editorReadKey();
+        if (c) {
+          E.mode = InputMode;
+          editorMoveCursor(ARROW_RIGHT);
+          editorDeleteChar();
+          editorInputKp(c);
+          E.mode = CommandMode;
+          editorMoveCursor(ARROW_LEFT);
+        }
+      }
+      break;
     case 'g':
       if (deleting) {
         int totlen = 0;