Implement proper font handling

minetest.conf.example

@@ -215,6 +215,8 @@
 #directional_colored_fog = true
 #tooltip_show_delay = 400
 # Delay showing tooltips, in miliseconds
+#screen_dpi = 72
+# adjust dpi configuration to your screen (PC/MAC only) e.g. for 4k screens
 
 # Default timeout for cURL, in milliseconds
 # Only has an effect if compiled with cURL