Improving command parsing semantics, gofmt, warn when command reported

src/text_editor/text_editor.cpp

@@ -460,6 +460,7 @@ void EvalCommand(String command) {
             return;
         }
     }
+    ReportErrorf("Failed to match with any of the commands: %S", command);
 }
 
 void EvalCommand(String16 command) {