support null title in .xoatrc

config.c

@@ -432,5 +432,11 @@ configure()
 		fclose(file);
 
 		regex_cache_empty();
+
+		if (settings.title && strcmp(settings.title, "null") == 0)
+		{
+			free(settings.title);
+			settings.title = NULL;
+		}
 	}
 }

xoatrc

@@ -11,7 +11,8 @@ border_focus Royal Blue
 border_blur Dark Gray
 border_urgent Red
 
-# Title bar xft font.
+# Title bar xft font. "null" means disable.
+# title null
 title sans:size=8
 title_blur Black
 title_focus White