Move scriptapi to separate folder (by sapier)

On the lua side, notably minetest.env:<function>(<args>) should now
be replaced by minetest.<function>(<args>).
The old way is and will stay supported for a long time.

Also:
Update and clean up lua_api.txt (by celeron55)
Move EnvRef to lua and remove add_rat and add_firefly (by kahrl)
Add separate src/util/CMakeLists.txt, other minor fixes (by kahrl)

src/scriptapi_particles.h

@@ -1,32 +0,0 @@
-/*
-Minetest-c55
-Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
-
-This program is free software; you can redistribute it and/or modify
-it under the terms of the GNU Lesser General Public License as published by
-the Free Software Foundation; either version 2.1 of the License, or
-(at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU Lesser General Public License for more details.
-
-You should have received a copy of the GNU Lesser General Public License along
-with this program; if not, write to the Free Software Foundation, Inc.,
-51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
-*/
-
-#ifndef LUA_PARTICLES_H_
-#define LUA_PARTICLES_H_
-
-extern "C" {
-#include <lua.h>
-#include <lauxlib.h>
-}
-
-int l_add_particle(lua_State *L);
-int l_add_particlespawner(lua_State *L);
-int l_delete_particlespawner(lua_State *L);
-
-#endif