Add alpha setting to font shadow

minetest.conf.example

@@ -213,6 +213,8 @@
 #font_size = 13
 # Font shadow offset, if 0 then shadow will not be drawn.
 #font_shadow = 1
+# Font shadow alpha (opaqueness, between 0 and 255)
+#font_shadow_alpha = 128
 #mono_font_path = fonts/liberationmono.ttf
 #mono_font_size = 13
 
@@ -220,6 +222,7 @@
 #fallback_font_path = fonts/DroidSansFallbackFull.ttf
 #fallback_font_size = 13
 #fallback_font_shadow = 1
+#fallback_font_shadow_alpha = 128
 
 #
 # Server stuff