Rename 'subgame' to 'game'

README.txt

 Minetest Game [minetest_game]
 =============================
-The main subgame for the Minetest engine
-========================================
+The main game for the Minetest engine
+=====================================
 
-To use this subgame with the Minetest engine, insert this repository as
+To use this game with the Minetest engine, insert this repository as
 	/games/minetest_game
 
 The Minetest engine can be found in:

game_api.txt

@@ -5,7 +5,7 @@ GitHub Repo: https://github.com/minetest/minetest_game
 Introduction
 ------------
 
-The Minetest Game subgame offers multiple new possibilities in addition to the Minetest engine's built-in API,
+The Minetest Game game offers multiple new possibilities in addition to the Minetest engine's built-in API,
 allowing you to add new plants to farming mod, buckets for new liquids, new stairs and custom panes.
 For information on the Minetest API, visit https://github.com/minetest/minetest/blob/master/doc/lua_api.txt
 Please note: