Add mods: technic, moreores, paintings, Nyancat (Pbj_pup). Small fix: sandwiches

mods/xcompat/doc/gameid.md

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+# GameId API
+
+## minetest versions >= 5.7 
+
+simply returns `minetest.get_game_info().id`  
+
+## minetest versions < 5.7
+
+approximates the gameid value via a hardcoded table of gameid=>modname 
+and then checks via `minetest.get_modpath()`. If it fails, it falls 
+back to using `xcompat_unknown_gameid` as the id. See the chart in the
+readme for which games are supported